RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
Hi Kevin, On Fri, May 04, 2012 at 03:02:16, Hilman, Kevin wrote: Ben Hutchings bhutchi...@solarflare.com writes: On Thu, 2012-05-03 at 19:25 +, Bedia, Vaibhav wrote: On Fri, May 04, 2012 at 00:16:32, Mark A. Greer wrote: [...] So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Recently I was thinking about how to get certain drivers to disallow some or all low power states and to me this also seems to fall in a similar category. One of the suggestions that I got was to check if the 'wakeup' entry associated with the device under sysfs could be leveraged for this. The PM code could maintain a whitelist (or blacklist) of devices and it decides the low power state to enter based on the 'wakeup' entries associated with these devices. In this particular case, maybe the driver could simply set this entry to non-wakeup capable when necessary and then let the PM code take care of skipping the wfi execution. Thoughts/brickbats welcome :) You can maybe (ab)use the pm_qos mechanism for this. I thought of using this too, but it doesn't actually solve the problem: Using PM QoS, you can avoid hitting the deeper idle states by setting a very low wakeup latency. However, on ARM platforms, even the shallowest idle states use the WFI instruction, and the EMAC would still not be able to wake the system from WFI. A possibility would be define the shallowest idle state to be one that doesn't call WFI and just does cpu_relax(). However, that would only work for CPUidle since PM QoS constraints are only checked by CPUidle. So, a non-CPUidle kernel would still have this bug. :( Ultimately, this is just broken HW. This network HW was bolted onto an existing SoC without consideration for wakeup capabilities. The result is that any use of this device with networking has to completely disable SoC power management. I was checking with internally with some folks on the issue being addressed in this patch and unfortunately no one seems to be aware of this :( Mark mentioned nfs mounted rootfs being slow but in my limited testing I didn't observe this on an AM3517 board. I am yet to go through the PSP code to be fully sure that wfi instruction is indeed being executed but I wanted to check if I need to do something specific to reproduce this at my end. Irrespective of the above problem being present in the h/w, I feel the approach of adding platform callbacks for blocking deeper idle states will create problems when this is required for multiple peripherals. I agree that the default behavior should be to support the deepest idle state based on the peripherals being used but IMO the user should have the flexibility to change this behavior if he wishes to do so. I don't know whether the usage of the 'wakeup' entries for giving this control to users qualifies as an abuse of the infrastructure. If it does, perhaps there should some other mechanism for letting users control the system behavior. Regards, Vaibhav -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
+Sekhar Bedia, Vaibhav vaibhav.be...@ti.com writes: Hi Kevin, On Fri, May 04, 2012 at 03:02:16, Hilman, Kevin wrote: Ben Hutchings bhutchi...@solarflare.com writes: On Thu, 2012-05-03 at 19:25 +, Bedia, Vaibhav wrote: On Fri, May 04, 2012 at 00:16:32, Mark A. Greer wrote: [...] So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Recently I was thinking about how to get certain drivers to disallow some or all low power states and to me this also seems to fall in a similar category. One of the suggestions that I got was to check if the 'wakeup' entry associated with the device under sysfs could be leveraged for this. The PM code could maintain a whitelist (or blacklist) of devices and it decides the low power state to enter based on the 'wakeup' entries associated with these devices. In this particular case, maybe the driver could simply set this entry to non-wakeup capable when necessary and then let the PM code take care of skipping the wfi execution. Thoughts/brickbats welcome :) You can maybe (ab)use the pm_qos mechanism for this. I thought of using this too, but it doesn't actually solve the problem: Using PM QoS, you can avoid hitting the deeper idle states by setting a very low wakeup latency. However, on ARM platforms, even the shallowest idle states use the WFI instruction, and the EMAC would still not be able to wake the system from WFI. A possibility would be define the shallowest idle state to be one that doesn't call WFI and just does cpu_relax(). However, that would only work for CPUidle since PM QoS constraints are only checked by CPUidle. So, a non-CPUidle kernel would still have this bug. :( Ultimately, this is just broken HW. This network HW was bolted onto an existing SoC without consideration for wakeup capabilities. The result is that any use of this device with networking has to completely disable SoC power management. I was checking with internally with some folks on the issue being addressed in this patch and unfortunately no one seems to be aware of this :( Do you mean they are not aware that the EMAC cannot wakeup th SoC, or they are not aware that having a device that cannot wakup the SoC has such an impact on Linux. Mark mentioned nfs mounted rootfs being slow but in my limited testing I didn't observe this on an AM3517 board. I am yet to go through the PSP code to be fully sure that wfi instruction is indeed being executed but I wanted to check if I need to do something specific to reproduce this at my end. Based on my discussion with Mark, I suspect that the kernel you're using is simply not going idle. Irrespective of the above problem being present in the h/w, I feel the approach of adding platform callbacks for blocking deeper idle states will create problems when this is required for multiple peripherals. I agree. If we have to do this for multiple peripherals, the curren approach it will become unwieldy. I agree that the default behavior should be to support the deepest idle state based on the peripherals being used but IMO the user should have the flexibility to change this behavior if he wishes to do so. Well, we always have the option of booting with 'nohlt' on the commandline. Since nobody seems to have thought about idle power management in the HW design, maybe we shouldn't break our backs to hack around the HW brokenness. Personally, I'm perfectly OK leaving the default behavior of sluggish/unresponsive devices that are not wakeup capable. The only fix is to not sleep, and that can be accomplished on the cmdline using nohlt (at the expense of some energy savings.) I don't know whether the usage of the 'wakeup' entries for giving this control to users qualifies as an abuse of the infrastructure. It does. If it does, perhaps there should some other mechanism for letting users control the system behavior. Come to think of it, the right solution here is probably to use runtime PM. We could then to add some custom hooks for davinci_emac in the device code to use enable_hlt/disable_hlt based on activity. In order to do that though, the davinci_emac driver needs to be runtime PM converted. Kevin -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Fri, May 04, 2012 at 01:55:58PM +, Bedia, Vaibhav wrote: Hi Vaibhav. Hi Kevin, On Fri, May 04, 2012 at 03:02:16, Hilman, Kevin wrote: Ben Hutchings bhutchi...@solarflare.com writes: On Thu, 2012-05-03 at 19:25 +, Bedia, Vaibhav wrote: On Fri, May 04, 2012 at 00:16:32, Mark A. Greer wrote: [...] So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Recently I was thinking about how to get certain drivers to disallow some or all low power states and to me this also seems to fall in a similar category. One of the suggestions that I got was to check if the 'wakeup' entry associated with the device under sysfs could be leveraged for this. The PM code could maintain a whitelist (or blacklist) of devices and it decides the low power state to enter based on the 'wakeup' entries associated with these devices. In this particular case, maybe the driver could simply set this entry to non-wakeup capable when necessary and then let the PM code take care of skipping the wfi execution. Thoughts/brickbats welcome :) You can maybe (ab)use the pm_qos mechanism for this. I thought of using this too, but it doesn't actually solve the problem: Using PM QoS, you can avoid hitting the deeper idle states by setting a very low wakeup latency. However, on ARM platforms, even the shallowest idle states use the WFI instruction, and the EMAC would still not be able to wake the system from WFI. A possibility would be define the shallowest idle state to be one that doesn't call WFI and just does cpu_relax(). However, that would only work for CPUidle since PM QoS constraints are only checked by CPUidle. So, a non-CPUidle kernel would still have this bug. :( Ultimately, this is just broken HW. This network HW was bolted onto an existing SoC without consideration for wakeup capabilities. The result is that any use of this device with networking has to completely disable SoC power management. I was checking with internally with some folks on the issue being addressed in this patch and unfortunately no one seems to be aware of this :( This is from the TI hardware engineer that I talked to after spending many hours trying to get the EMAC to wake up the system. It was a private conversation so I won't share his name/email here. If you want to contact him, please reach me privately. No, AM35x can't be waken up from CPGMAC. If customer need to wake AM35x up from Ethernet, a wake up interrupt signal from Ethernet phy should be connected to one of wakeup capable GPIO pins. Mark mentioned nfs mounted rootfs being slow but in my limited testing I didn't observe this on an AM3517 board. I am yet to go through the PSP code to be fully sure that wfi instruction is indeed being executed but I wanted to check if I need to do something specific to reproduce this at my end. When you go through the PSP code, look for the definition use of omap3_can_sleep(). That routine returns '0' when either cpu_is_omap3505() or cpu_is_omap3517() ruturns true (among other conditions). You will see that its used in omap3_pm_idle() to exit early so pm_idle never executes the wfi. I expect that you don't have CONFIG_CPU_IDLE enabled, so cpuidle has no opportunity to execute a wfi. If it is enabled, omap3_can_sleep() is used in omap3_idle_bm_check() which is used in omap3_enter_idle_bm() so the wfi won't be executed when omap3_enter_idle_bm() is called. omap3_enter_idle() isn't called (in my testing--the code is very different from current k.o.) so it doesn't execute the wfi either. Therefore, you don't see an issue when running PSP code. Irrespective of the above problem being present in the h/w, I feel the approach of adding platform callbacks for blocking deeper idle states will create problems when this is required for multiple peripherals. I agree that the default behavior should be to support the deepest idle state based on the peripherals being used but IMO the user should have the flexibility to change this behavior if he wishes to do so. I agree but hopefully this doesn't become common. The real issue is a missing hardware feature that--again, hopefully--won't become common. Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
Hi Mark, Mark A. Greer mgr...@animalcreek.com writes: [...] To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. OK, I'm feeling rather dumb for not thinking of this before and suggesting that you use pdata callbacks. But there is a better solution: runtime PM. I hadn't noticed before that since this driver comes from davinci, it uses the clock API and not runtime PM which all OMAP drivers have been (or are being) converted to. If we replace the clock API usage in this driver with proper runtime PM usage, we can make this work. Basically, clk_enable() turns into pm_runtime_get_sync() and clk_disable() turns into pm_runtime_put(). With that, the OMAP PM core will get callbacks whenever the device is [not] needed and we can use device-specific hooks to call disable_hlt/enable_hlt. The only catch though is that in order for this driver to be converted to runtime PM and still work on davinci devices, the davinci kernel needs to grow runtime PM support. I belive Sekhar is already looking into this, and OMAP1 (mach-omap1/pm_bus.c) will be a good example of how to get a basic runtime PM implementation working for davinci which just does basic clock management. Having worked on the guts of runtime PM for OMAP, I know it pretty well (which is all the more embarrasing that I didn't think of suggesting it sooner.) So, let me know how I can help. As a quick hack to test my idea will help, you can try simply calling disable_hlt() after clk_enable() and enable_hlt() after clk_disable() in teh davinci_emac driver. That will effectively be what happens after a runtime PM conversion with device-specific hooks. The (not even compile tested) patch below does this. For starters, can you tell me if this results in normal performance on the EMAC? Kevin diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c index 174a334..c92bc28 100644 --- a/drivers/net/ethernet/ti/davinci_emac.c +++ b/drivers/net/ethernet/ti/davinci_emac.c @@ -1909,6 +1909,7 @@ static int __devinit davinci_emac_probe(struct platform_device *pdev) netif_napi_add(ndev, priv-napi, emac_poll, EMAC_POLL_WEIGHT); clk_enable(emac_clk); + disable_hlt(); /* register the network device */ SET_NETDEV_DEV(ndev, pdev-dev); @@ -1929,6 +1930,7 @@ static int __devinit davinci_emac_probe(struct platform_device *pdev) netdev_reg_err: clk_disable(emac_clk); + enable_hlt(); no_irq_res: if (priv-txchan) cpdma_chan_destroy(priv-txchan); @@ -1979,6 +1981,7 @@ static int __devexit davinci_emac_remove(struct platform_device *pdev) clk_disable(emac_clk); clk_put(emac_clk); + enable_hlt(); return 0; } -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Fri, May 04, 2012 at 07:31:30AM -0700, Kevin Hilman wrote: Bedia, Vaibhav vaibhav.be...@ti.com writes: Hi Kevin. If it does, perhaps there should some other mechanism for letting users control the system behavior. Come to think of it, the right solution here is probably to use runtime PM. We could then to add some custom hooks for davinci_emac in the device code to use enable_hlt/disable_hlt based on activity. That was my first thought, actually, but that only works if its okay for the driver to call enable_hlt/disable_hlt directly (i.e., have runtime_suspend() call enable_hlt() and runtime_resume() call disable_hlt()). However, I assumed it would _not_ be acceptable for the driver to issue those calls directly. Its a platform-specific issue that we shouldn't be polluting the driver with and there are currently no drivers that call them under the drivers directory. If its not okay to call enable_hlt/disable_hlt directly, then we still need callback hooks to the plaform code (i.e., some version of this patch). In order to do that though, the davinci_emac driver needs to be runtime PM converted. We probably should pm_runtime-ize the driver either way but we need to resolve the question of whether its okay for the driver to call enable_hlt/disable_hlt directly or not. If it is okay, we call them in runtime_suspend/resume. If it isn't okay, then we still need platform callback hooks. Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Fri, May 04, 2012 at 09:44:45AM -0700, Kevin Hilman wrote: Hi Mark, Hi Kevin. Mark A. Greer mgr...@animalcreek.com writes: [...] To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. OK, I'm feeling rather dumb for not thinking of this before and suggesting that you use pdata callbacks. But there is a better solution: runtime PM. I hadn't noticed before that since this driver comes from davinci, it uses the clock API and not runtime PM which all OMAP drivers have been (or are being) converted to. If we replace the clock API usage in this driver with proper runtime PM usage, we can make this work. Basically, clk_enable() turns into pm_runtime_get_sync() and clk_disable() turns into pm_runtime_put(). With that, the OMAP PM core will get callbacks whenever the device is [not] needed and we can use device-specific hooks to call disable_hlt/enable_hlt. The only catch though is that in order for this driver to be converted to runtime PM and still work on davinci devices, the davinci kernel needs to grow runtime PM support. I belive Sekhar is already looking into this, and OMAP1 (mach-omap1/pm_bus.c) will be a good example of how to get a basic runtime PM implementation working for davinci which just does basic clock management. Having worked on the guts of runtime PM for OMAP, I know it pretty well (which is all the more embarrasing that I didn't think of suggesting it sooner.) So, let me know how I can help. As a quick hack to test my idea will help, you can try simply calling disable_hlt() after clk_enable() and enable_hlt() after clk_disable() in teh davinci_emac driver. That will effectively be what happens after a runtime PM conversion with device-specific hooks. The (not even compile tested) patch below does this. For starters, can you tell me if this results in normal performance on the EMAC? No worries. I thought of pm_runtime before embarking on this patch, actually. I explained why I did this patch anyaway in another email-- our emails crossed in the ether. diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c index 174a334..c92bc28 100644 --- a/drivers/net/ethernet/ti/davinci_emac.c +++ b/drivers/net/ethernet/ti/davinci_emac.c @@ -1909,6 +1909,7 @@ static int __devinit davinci_emac_probe(struct platform_device *pdev) netif_napi_add(ndev, priv-napi, emac_poll, EMAC_POLL_WEIGHT); clk_enable(emac_clk); + disable_hlt(); /* register the network device */ SET_NETDEV_DEV(ndev, pdev-dev); @@ -1929,6 +1930,7 @@ static int __devinit davinci_emac_probe(struct platform_device *pdev) netdev_reg_err: clk_disable(emac_clk); + enable_hlt(); no_irq_res: if (priv-txchan) cpdma_chan_destroy(priv-txchan); @@ -1979,6 +1981,7 @@ static int __devexit davinci_emac_remove(struct platform_device *pdev) clk_disable(emac_clk); clk_put(emac_clk); + enable_hlt(); return 0; } Yes, this works (it essentially does what my patches do except I did the calls in open/stop instead of probe/remove :). Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
Mark A. Greer mgr...@animalcreek.com writes:
On Fri, May 04, 2012 at 07:31:30AM -0700, Kevin Hilman wrote:
[...]
Come to think of it, the right solution here is probably to use runtime
PM. We could then to add some custom hooks for davinci_emac in the
device code to use enable_hlt/disable_hlt based on activity.
That was my first thought, actually, but that only works if its
okay for the driver to call enable_hlt/disable_hlt directly (i.e.,
have runtime_suspend() call enable_hlt() and runtime_resume() call
disable_hlt()). However, I assumed it would _not_ be acceptable for
the driver to issue those calls directly.
I agree.
Its a platform-specific issue that we shouldn't be polluting the
driver with and there are currently no drivers that call them under
the drivers directory.
Using runtime PM we don't have to have any platform specific calls in
the driver. We handle it inside the platform-specific runtime PM
implementation.
IOW, we don't have to call enable_hlt/disable_hlt in the driver. It can
be completely transparent to the driver. We can call
enable_hlt/disable_hlt in device specific code. That way, davinci
platforms with this same IP won't use
To demonstrate, assume the davinci_emac is runtime PM converted and does
a pm_runtime_get_sync() instead of clk_enable().
For the first call to pm_runtime_get_sync() (when runtime PM count goes
from zero to 1), this will trigger the runtime PM core to runtime PM
enable the device. Using the driver model's 'PM domain' layer, we've
plugged in our omap_device layer, so the omap_device layer is called for
runtime PM transitions. (c.f. omap_device_pm_domain in plat-omap/omap_device.c)
Specifically, on a a runtime PM 'get', the PM domain's
-runtime_resume() callback is called. For an omap_device, that is
_od_runtime_resume(). After enabling the device using
omap_device_enable() the driver's -runtime_resume callback is called.
So, to summarize, the (simplified) flow looks like this:
pm_runtime_get_sync()
PM domain-runtime_resume() /* _od_runtime_resume() */
omap_device_enable()
pm_generic_runtime_resume()
driver-runtime_resume()
However, you're still wondering where we would sneak in the call to
disable_hlt. Well, I'm glad you asked
Looking closer at omap_device_enable(), you'll see that it calls
_omap_device_activate() which uses a function pointer in the
omap_device_pm_latency structure to actually enable the device.
By default, this function is omap_device_enable_hwmods() for all
omap_devices, which in turn uses the hwmod layer to enable the HW
(including clock enable, PM init, etc.)
Now, here's the magic
On a per-device basis, that activate function can be customized. In the
custom function, you can add custom calls (e.g. disable_hlt) and then
call the normal omap_device_* functions to continue the default
behavior.
This is getting messy, so let me give a concrete example in the form of
a patch. Starting from the GPIO driver, which is already runtime PM
converted. If I wanted to add disable_hlt/enable_hlt whenver the device
is runtime PM enabled/disabled, it would be as simple as the patch below.
So in summary, whever pm_runtime_get_sync() is called (and the usecount
goes from zero to 1), the omap_device 'activate' function is called
(which can call disable_hlt()), and whenever pm_runtime_put() is called
(and the usecount reaches zero), the omap_device 'deactivate' function
is called, and enable_hlt() can be called.
The example I give below customizes the hooks for *all* SoCs, but in the
specific case we're trying to solve, we would only need to add custom
hooks for the devices without wakeups.
Note that all of this presumes that the driver is runtime PM converted
*and* the device itself is built using omap_device_build(). That means
that the device init code in am35xx_emac.c needs to be converted to use
omap_device_build instead of the normal platform_device_* calls. (note
though that omap_device_build() will also create/register the
platform_device.
Kevin
diff --git a/arch/arm/mach-omap2/gpio.c b/arch/arm/mach-omap2/gpio.c
index a80e093..3acd1eb 100644
--- a/arch/arm/mach-omap2/gpio.c
+++ b/arch/arm/mach-omap2/gpio.c
@@ -26,8 +26,30 @@
#include plat/omap_device.h
#include plat/omap-pm.h
+#include asm/system.h
+
#include powerdomain.h
+static int omap2_gpio_deactivate_func(struct omap_device *od)
+{
+ enable_hlt();
+ return omap_device_idle_hwmods(od);
+}
+
+static int omap2_gpio_activate_func(struct omap_device *od)
+{
+ disable_hlt();
+ return omap_device_enable_hwmods(od);
+}
+
+struct omap_device_pm_latency pm_lats[] __initdata = {
+ {
+ .activate_func = omap2_gpio_activate_func,
+ .deactivate_func = omap2_gpio_deactivate_func,
+ .flags = OMAP_DEVICE_LATENCY_AUTO_ADJUST,
+ },
+};
+
static int __init omap2_gpio_dev_init(struct omap_hwmod *oh, void *unused)
{
struct
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Fri, May 04, 2012 at 02:02:43PM -0700, Kevin Hilman wrote: Mark A. Greer mgr...@animalcreek.com writes: On Fri, May 04, 2012 at 07:31:30AM -0700, Kevin Hilman wrote: [...] Come to think of it, the right solution here is probably to use runtime PM. We could then to add some custom hooks for davinci_emac in the device code to use enable_hlt/disable_hlt based on activity. That was my first thought, actually, but that only works if its okay for the driver to call enable_hlt/disable_hlt directly (i.e., have runtime_suspend() call enable_hlt() and runtime_resume() call disable_hlt()). However, I assumed it would _not_ be acceptable for the driver to issue those calls directly. I agree. Its a platform-specific issue that we shouldn't be polluting the driver with and there are currently no drivers that call them under the drivers directory. Using runtime PM we don't have to have any platform specific calls in the driver. We handle it inside the platform-specific runtime PM implementation. FYI, with some further discussion via IRC, I'm going to implement what Kevin has laid out here. There is a dependency on davinci adding support too but I'll coordinate with the people/person doing that. Please disregard this patch. Thanks for the help everyone. Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: From: Mark A. Greer mgr...@animalcreek.com The davinci EMAC driver has been incorporated into the am35x family of SoC's which is OMAP-based. The incorporation is incomplete in that the EMAC cannot unblock the [ARM] core if its blocked on a 'wfi' instruction. This is an issue with the cpu_idle code because it has the core execute a 'wfi' instruction. To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. It is not sufficient to simply call disable_hlt() when there is an EMAC present because it could be present but not actually used in which case, we do want the 'wfi' to be executed. Are you trying to say that if ARM executes _just_ wfi and _absolutely nothing else_ is done in the OMAP PM code, EMAC stops working? However, if this is indeed the case, then probably a better solution would be to invoke disable_hlt() from the board file when EMAC support is compiled in. Regards, Vaibhav -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
Bedia, Vaibhav vaibhav.be...@ti.com writes: On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: From: Mark A. Greer mgr...@animalcreek.com The davinci EMAC driver has been incorporated into the am35x family of SoC's which is OMAP-based. The incorporation is incomplete in that the EMAC cannot unblock the [ARM] core if its blocked on a 'wfi' instruction. This is an issue with the cpu_idle code because it has the core execute a 'wfi' instruction. To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. It is not sufficient to simply call disable_hlt() when there is an EMAC present because it could be present but not actually used in which case, we do want the 'wfi' to be executed. Are you trying to say that if ARM executes _just_ wfi and _absolutely nothing else_ is done in the OMAP PM code, EMAC stops working? However, if this is indeed the case, then probably a better solution would be to invoke disable_hlt() from the board file when EMAC support is compiled in. No. As Mark stated in the changelog, doing that will prevent any low-power states states even if the EMAC is not in use. IMO, it is best to only prevent WFI when absolutely needed. Kevin -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Thu, May 03, 2012 at 10:44:44AM +, Bedia, Vaibhav wrote: On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: From: Mark A. Greer mgr...@animalcreek.com The davinci EMAC driver has been incorporated into the am35x family of SoC's which is OMAP-based. The incorporation is incomplete in that the EMAC cannot unblock the [ARM] core if its blocked on a 'wfi' instruction. This is an issue with the cpu_idle code because it has the core execute a 'wfi' instruction. To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. It is not sufficient to simply call disable_hlt() when there is an EMAC present because it could be present but not actually used in which case, we do want the 'wfi' to be executed. Are you trying to say that if ARM executes _just_ wfi and _absolutely nothing else_ is done in the OMAP PM code, EMAC stops working? No, I'm saying the EMAC can't wake the core from the wfi so if nothing else happens in the system, its effectively hung. If something else does happen in the system (e.g., a timer expires), the the system is extremely slow because because its only waking up when a timer (or something else wakes it up--but not net traffic). This is very apparent when using an nfs-mounted rootfs. It doesn't hang but its extremely slow because occasionally something else wakes up the core but it spends most of its time stuck in the wfi when it should be handling net/nfs traffic. However, if this is indeed the case, then probably a better solution would be to invoke disable_hlt() from the board file when EMAC support is compiled in. Kevin addressed this one. Thanks Kevin. Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Thu, May 03, 2012 at 21:39:18, Mark A. Greer wrote: On Thu, May 03, 2012 at 10:44:44AM +, Bedia, Vaibhav wrote: On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: From: Mark A. Greer mgr...@animalcreek.com The davinci EMAC driver has been incorporated into the am35x family of SoC's which is OMAP-based. The incorporation is incomplete in that the EMAC cannot unblock the [ARM] core if its blocked on a 'wfi' instruction. This is an issue with the cpu_idle code because it has the core execute a 'wfi' instruction. To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. It is not sufficient to simply call disable_hlt() when there is an EMAC present because it could be present but not actually used in which case, we do want the 'wfi' to be executed. Are you trying to say that if ARM executes _just_ wfi and _absolutely nothing else_ is done in the OMAP PM code, EMAC stops working? No, I'm saying the EMAC can't wake the core from the wfi so if nothing else happens in the system, its effectively hung. If something else does happen in the system (e.g., a timer expires), the the system is extremely slow because because its only waking up when a timer (or something else wakes it up--but not net traffic). This is very apparent when using an nfs-mounted rootfs. It doesn't hang but its extremely slow because occasionally something else wakes up the core but it spends most of its time stuck in the wfi when it should be handling net/nfs traffic. So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Thu, May 03, 2012 at 06:21:27PM +, Bedia, Vaibhav wrote: On Thu, May 03, 2012 at 21:39:18, Mark A. Greer wrote: On Thu, May 03, 2012 at 10:44:44AM +, Bedia, Vaibhav wrote: On Thu, May 03, 2012 at 05:17:18, Mark A. Greer wrote: From: Mark A. Greer mgr...@animalcreek.com The davinci EMAC driver has been incorporated into the am35x family of SoC's which is OMAP-based. The incorporation is incomplete in that the EMAC cannot unblock the [ARM] core if its blocked on a 'wfi' instruction. This is an issue with the cpu_idle code because it has the core execute a 'wfi' instruction. To work around this issue, add platform data callbacks which are called at the beginning of the open routine and at the end of the stop routine of the davinci_emac driver. The callbacks allow the platform code to issue disable_hlt() and enable_hlt() calls appropriately. Calling disable_hlt() prevents cpu_idle from issuing the 'wfi' instruction. It is not sufficient to simply call disable_hlt() when there is an EMAC present because it could be present but not actually used in which case, we do want the 'wfi' to be executed. Are you trying to say that if ARM executes _just_ wfi and _absolutely nothing else_ is done in the OMAP PM code, EMAC stops working? No, I'm saying the EMAC can't wake the core from the wfi so if nothing else happens in the system, its effectively hung. If something else does happen in the system (e.g., a timer expires), the the system is extremely slow because because its only waking up when a timer (or something else wakes it up--but not net traffic). This is very apparent when using an nfs-mounted rootfs. It doesn't hang but its extremely slow because occasionally something else wakes up the core but it spends most of its time stuck in the wfi when it should be handling net/nfs traffic. So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Mark -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Fri, May 04, 2012 at 00:16:32, Mark A. Greer wrote: [...] So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Recently I was thinking about how to get certain drivers to disallow some or all low power states and to me this also seems to fall in a similar category. One of the suggestions that I got was to check if the 'wakeup' entry associated with the device under sysfs could be leveraged for this. The PM code could maintain a whitelist (or blacklist) of devices and it decides the low power state to enter based on the 'wakeup' entries associated with these devices. In this particular case, maybe the driver could simply set this entry to non-wakeup capable when necessary and then let the PM code take care of skipping the wfi execution. Thoughts/brickbats welcome :) Regards, Vaibhav -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [PATCH] net: davinci_emac: Add pre_open, post_stop platform callbacks
On Thu, 2012-05-03 at 19:25 +, Bedia, Vaibhav wrote: On Fri, May 04, 2012 at 00:16:32, Mark A. Greer wrote: [...] So, if I understood this correctly, it's effectively like blocking a low power state transition (here wfi execution) when EMAC is active? Assuming it is my patch, correct. Recently I was thinking about how to get certain drivers to disallow some or all low power states and to me this also seems to fall in a similar category. One of the suggestions that I got was to check if the 'wakeup' entry associated with the device under sysfs could be leveraged for this. The PM code could maintain a whitelist (or blacklist) of devices and it decides the low power state to enter based on the 'wakeup' entries associated with these devices. In this particular case, maybe the driver could simply set this entry to non-wakeup capable when necessary and then let the PM code take care of skipping the wfi execution. Thoughts/brickbats welcome :) You can maybe (ab)use the pm_qos mechanism for this. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
