On 20-06-09 11:27, Andrzej Hajda wrote: > > On 09.06.2020 08:45, Marco Felsch wrote: > > 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. > > > I have looked at the drivers and I see the main issue I see is that imx > drivers performs resource acquisition in bind phase.
As I said we are working on this. > I think rule of > thumb should be "do not expose yourself, until you are ready", which in > this case means "do not call component_add, until resources are > acquired" - ie resource acquisition should be performed in probe. Hm.. there are is no documentation which forbid this use-case. I thought that the component framework bind() equals the driver probe() function.. > I use > this approach mainly to avoid multiple deferred re-probes, but it should > solve also this issue, so even if there will be solution to "deferred > probe issues" in core it would be good to fix imx drivers. Pls, see my above comments. It is not only the imx driver. Also we shouldn't expect that driver-developers will follow a rule which is not written somewhere. Regards, Marco > Regards > > Andrzej > > > > > > 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? > >>>>