exynos-drm registration: infinite loop

[Andrzej Hajda]

On 11/06/2014 07:23 AM, Inki Dae wrote:
> 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.

It is enough to check if there are platform devices compatible with
drivers registered by exynos_drm_dev.

Regards
Andrzej

> 
> Thanks,
> Inki Dae
> 
>> Thierry
>>
>>
>>
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