exynos-drm registration: infinite loop

[Inki Dae]

On 2014년 11월 06일 17:03, Andrzej Hajda wrote:
> 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.
> 

Yes, we can do it simply. However, I'm not still clear to handle these
issues in this manner because if we use the super device which is the
most generic way then Exynos drm can have real device node so we don't
need such exception codes anymore. And with the super device, I'm not
sure whether there are other issues or not we can face but it would be
enough to consider only generic ways.

Anyway, I will decide how to handle Exynos drm device after listening to
more other opinions.

Thanks,
Inki Dae

> Regards
> Andrzej
> 
>>
>> Thanks,
>> Inki Dae
>>
>>> Thierry
>>>
>>>
>>>
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