exynos-drm registration: infinite loop

[Inki Dae]

On 2014년 11월 05일 23:38, Thierry Reding wrote:
> On Tue, Nov 04, 2014 at 09:18:46PM +0400, Matwey V. Kornilov wrote:
>> Hi,
>>
>> I run 3.18-rc3 kernel on BeagleBone Black. It doesn't have Exynos DRM
>> of course, but I run multi-platform kernel where CONFIG_DRM_EXYNOS is
>> set to 'y'.
>> The issue here is that the platform probe/init goes to infinite loop
>> as the following:
>>
>> [    5.717343] platform exynos-drm: Driver exynos-drm requests probe deferral
>> [    5.726848] exynos-drm-ipp exynos-drm-ipp: drm ipp registered successfully.
>> [    5.734700] platform exynos-drm: Driver exynos-drm requests probe deferral
>> [    5.744044] exynos-drm-ipp exynos-drm-ipp: drm ipp registered successfully.
>> [    5.752010] platform exynos-drm: Driver exynos-drm requests probe deferral
>> [    5.761377] exynos-drm-ipp exynos-drm-ipp: drm ipp registered successfully.
>> [    5.769291] platform exynos-drm: Driver exynos-drm requests probe deferral
>>
>> It is quite unexpectable behavior. I would expect that the exynos-drm
>> failed to initialize with 'no device' error.
>>
>> See also for the reference: https://bugzilla.kernel.org/show_bug.cgi?id=87691
> 
> The reason for this seems to be that Exynos DRM instantiates a dummy
> device that it can bind to (see exynos_drm_init()). Now this code is
> executed unconditonally, so the device will be created whether or not
> the kernel/module runs on an Exynos SoC. The driver should really bind
> to some real device rather than instantiating a dummy. Or if it must
> bind to a dummy then the code needs to at least check that it's running
> on an Exynos SoC before instantiating the dummy.
> 

Right, I also think the problem is because we use a dummay device for
Exynos drm. As you mentioned, this device can always be bound as long as
Exynos drm driver is enabled even without real device. So this issue
gives us that we need super device node again. Actually, I had already
tried the use  of the super device node like below for Exynos drm but
other Samsung guys didn't want to use it.
	http://lists.freedesktop.org/archives/dri-devel/2014-April/056618.html

I think now we have the reason that we should use super device node so I
will try to support the super device for Exynos drm like other ARM drm
drivers did. However, for this, I'd like to listen to other opinions
for a while before that.

Thanks,
Inki Dae

> Thierry
> 
> 
> 
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