On 20-06-08 13:11, Andrzej Hajda wrote: > > On 08.06.2020 11:17, Marco Felsch wrote: > > On 20-03-26 18:31, Andy Shevchenko wrote: > >> On Thu, Mar 26, 2020 at 03:01:22PM +0000, Grant Likely wrote: > >>> On 25/03/2020 12:51, Andy Shevchenko wrote: > >>>> On Tue, Mar 24, 2020 at 08:29:01PM -0700, Saravana Kannan wrote: > >>>>> On Tue, Mar 24, 2020 at 5:38 AM Andy Shevchenko > >>>>> <andriy.shevche...@linux.intel.com> wrote: > >>>>>> Consider the following scenario. > >>>>>> > >>>>>> The main driver of USB OTG controller (dwc3-pci), which has the > >>>>>> following > >>>>>> functional dependencies on certain platform: > >>>>>> - ULPI (tusb1210) > >>>>>> - extcon (tested with extcon-intel-mrfld) > >>>>>> > >>>>>> Note, that first driver, tusb1210, is available at the moment of > >>>>>> dwc3-pci probing, while extcon-intel-mrfld is built as a module and > >>>>>> won't appear till user space does something about it. > >>>>>> > >>>>>> This is depicted by kernel configuration excerpt: > >>>>>> > >>>>>> CONFIG_PHY_TUSB1210=y > >>>>>> CONFIG_USB_DWC3=y > >>>>>> CONFIG_USB_DWC3_ULPI=y > >>>>>> CONFIG_USB_DWC3_DUAL_ROLE=y > >>>>>> CONFIG_USB_DWC3_PCI=y > >>>>>> CONFIG_EXTCON_INTEL_MRFLD=m > >>>>>> > >>>>>> In the Buildroot environment the modules are probed by alphabetical > >>>>>> ordering > >>>>>> of their modaliases. The latter comes to the case when USB OTG driver > >>>>>> will be > >>>>>> probed first followed by extcon one. > >>>>>> > >>>>>> So, if the platform anticipates extcon device to be appeared, in the > >>>>>> above case > >>>>>> we will get deferred probe of USB OTG, because of ordering. > >>>>>> > >>>>>> Since current implementation, done by the commit 58b116bce136 > >>>>>> ("drivercore: > >>>>>> deferral race condition fix") counts the amount of triggered deferred > >>>>>> probe, > >>>>>> we never advance the situation -- the change makes it to be an > >>>>>> infinite loop. > >>>>> Hi Andy, > >>>>> > >>>>> I'm trying to understand this sequence of steps. Sorry if the questions > >>>>> are stupid -- I'm not very familiar with USB/PCI stuff. > >>>> Thank you for looking into this. My answer below. > >>>> > >>>> As a first thing I would like to tell that there is another example of > >>>> bad > >>>> behaviour of deferred probe with no relation to USB. The proposed change > >>>> also > >>>> fixes that one (however, less possible to find in real life). > >>>> > >>>>>> ---8<---8<--- > >>>>>> > >>>>>> [ 22.187127] driver_deferred_probe_trigger <<< 1 > >>>>>> > >>>>>> ...here is the late initcall triggers deferred probe... > >>>>>> > >>>>>> [ 22.191725] platform dwc3.0.auto: deferred_probe_work_func in > >>>>>> deferred list > >>>>>> > >>>>>> ...dwc3.0.auto is the only device in the deferred list... > >>>>> Ok, dwc3.0.auto is the only unprobed device at this point? > >>>> Correct. > >>>> > >>>>>> [ 22.198727] platform dwc3.0.auto: deferred_probe_work_func 1 <<< > >>>>>> counter 1 > >>>>>> > >>>>>> ...the counter before mutex is unlocked is kept the same... > >>>>>> > >>>>>> [ 22.205663] platform dwc3.0.auto: Retrying from deferred list > >>>>>> > >>>>>> ...mutes has been unlocked, we try to re-probe the driver... > >>>>>> > >>>>>> [ 22.211487] bus: 'platform': driver_probe_device: matched device > >>>>>> dwc3.0.auto with driver dwc3 > >>>>>> [ 22.220060] bus: 'platform': really_probe: probing driver dwc3 with > >>>>>> device dwc3.0.auto > >>>>>> [ 22.238735] bus: 'ulpi': driver_probe_device: matched device > >>>>>> dwc3.0.auto.ulpi with driver tusb1210 > >>>>>> [ 22.247743] bus: 'ulpi': really_probe: probing driver tusb1210 with > >>>>>> device dwc3.0.auto.ulpi > >>>>>> [ 22.256292] driver: 'tusb1210': driver_bound: bound to device > >>>>>> 'dwc3.0.auto.ulpi' > >>>>>> [ 22.263723] driver_deferred_probe_trigger <<< 2 > >>>>>> > >>>>>> ...the dwc3.0.auto probes ULPI, we got successful bound and bumped > >>>>>> counter... > >>>>>> > >>>>>> [ 22.268304] bus: 'ulpi': really_probe: bound device > >>>>>> dwc3.0.auto.ulpi to driver tusb1210 > >>>>> So where did this dwc3.0.auto.ulpi come from? > >>>>> Looks like the device is created by dwc3_probe() through this call flow: > >>>>> dwc3_probe() -> dwc3_core_init() -> dwc3_core_ulpi_init() -> > >>>>> dwc3_ulpi_init() -> ulpi_register_interface() -> ulpi_register() > >>>> Correct. > >>>> > >>>>>> [ 22.276697] platform dwc3.0.auto: Driver dwc3 requests probe > >>>>>> deferral > >>>>> Can you please point me to which code patch actually caused the probe > >>>>> deferral? > >>>> Sure, it's in drd.c. > >>>> > >>>> if (device_property_read_string(dev, "linux,extcon-name", &name) == 0) { > >>>> edev = extcon_get_extcon_dev(name); > >>>> if (!edev) > >>>> return ERR_PTR(-EPROBE_DEFER); > >>>> return edev; > >>>> } > >>>> > >>>>>> ...but extcon driver is still missing... > >>>>>> > >>>>>> [ 22.283174] platform dwc3.0.auto: Added to deferred list > >>>>>> [ 22.288513] platform dwc3.0.auto: driver_deferred_probe_add_trigger > >>>>>> local counter: 1 new counter 2 > >>>>> I'm not fully aware of all the USB implications, but if extcon is > >>>>> needed, why can't that check be done before we add and probe the ulpi > >>>>> device? That'll avoid this whole "fake" probing and avoid the counter > >>>>> increase. And avoid the need for this patch that's touching the code > >>>>> code that's already a bit delicate. > >>>>> Also, with my limited experience with all the possible drivers in the > >>>>> kernel, it's weird that the ulpi device is added and probed before we > >>>>> make sure the parent device (dwc3.0.auto) can actually probe > >>>>> successfully. > >>>> As I said above the deferred probe trigger has flaw on its own. > >>>> Even if we fix for USB case, there is (and probably will be) others. > >>> Right here is the driver design bug. A driver's probe() hook should *not* > >>> return -EPROBE_DEFER after already creating child devices which may have > >>> already been probed. > >> Any documentation statement for this requirement? > >> > >> By the way, I may imagine other mechanisms that probe the driver on other > >> CPU > >> at the same time (let's consider parallel modprobes). The current code has > >> a > >> flaw with that. > > Hi, > > > > sorry for picking this up again but I stumbled above the same issue > > within the driver imx/drm driver which is using the component framework. > > I end up in a infinity boot loop if I enabled the HDMI (which is the > > DesignWare bridge device) and the LVDS support and the LVDS bind return > > with EPROBE_DEFER. There are no words within the component framework docs > > which says that this is forbidden. Of course we can work-around the > > driver-core framework but IMHO this shouldn't be the way to go. I do not > > say that we should revert the commit introducing the regression but we > > should address this not only by extending the docs since the most > > drm-drivers are using the component framework and can end up in the same > > situation. > > I am not sure why do you think this is similar issue.
Because I see trying to bind the device over and over.. > Please describe the issue in more detail. Which drivers defers probe and > why, and why do you have infinite loop. As said I'm currently on the imx-drm driver. The iMX6 devices are using the synopsis HDMI IP core and so they are using this bridge device driver (drivers/gpu/drm/bridge/synopsys/). The imx-drm driver can be build module wise. As example I enabled the LDB and the HDMI support. The HDMI driver is composed as platform driver with different (sub-)drivers and devices. Those devices are populated by the HDMI core driver _probe() function and triggers a driver_deferred_probe_trigger() after the driver successfully probed. The LDB driver bind() returns -EPROBE_DEFER because the panel we are looking for depends on a defered regulator device. Now the defered probe code tries to probe the defered devices again because the local-trigger count was changed by the HDMI driver and we are in the never ending loop. > In general deferring probe from bind is not forbidden, but it should be > used carefully (as everything in kernel :) ). Fixing deferring probe > issues in many cases it is a matter of figuring out 'dependency loops' > and breaking them by splitting device initialization into more than one > phase. We are on the way of splitting the imx-drm driver but there are many other DRM drivers using the component framework. As far as I can see the sunxi8 driver is component based and uses the same HDMI driver. I'm with Andy that we should fix that on the common/core place. Regards, Marco > Regards > > Andrzej > > > > > >>> It can be solved by refactoring the driver probe routine. If a resource is > >>> required to be present, then check that it is available early; before > >>> registering child devices. > >> We fix one and leave others. > > E.g. the imx-drm and the sunxi driver... > > > > Regards, > > Marco > > > >>> The proposed solution to modify driver core is fragile and susceptible to > >>> side effects from other probe paths. I don't think it is the right > >>> approach. > >> Have you tested it on your case? Does it fix the issue? > >> > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |