linux-kernel - Re: [PATCH v3] drm/gma500: depend on framebuffer

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Date:   Thu, 21 Apr 2022 15:22:55 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Patrik Jakobsson <patrik.r.jakobsson@...il.com>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        James Hilliard <james.hilliard1@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v3] drm/gma500: depend on framebuffer

On 4/21/22 14:54, Patrik Jakobsson wrote:
> On Thu, Apr 21, 2022 at 2:47 PM Javier Martinez Canillas
> <javierm@...hat.com> wrote:

[snip]

>>>>> diff --git a/drivers/gpu/drm/gma500/Kconfig b/drivers/gpu/drm/gma500/Kconfig
>>>>> index 0cff20265f97..a422fa84d53b 100644
>>>>> --- a/drivers/gpu/drm/gma500/Kconfig
>>>>> +++ b/drivers/gpu/drm/gma500/Kconfig
>>>>> @@ -2,11 +2,13 @@
>>>>>   config DRM_GMA500
>>>>>       tristate "Intel GMA500/600/3600/3650 KMS Framebuffer"
>>>>>       depends on DRM && PCI && X86 && MMU
>>>>> +     depends on FB
>>>>
>>>> Why do we need FB here? Framebuffer support should be hidden by DRM's
>>>> fbdev helpers.
>>>
>>> It is not needed but gives him video output since it enables the drm
>>> fbdev emulation.
>>>
>>
>> I'm not sure to understand this. Shouldn't depend on DRM_FBDEV_EMULATION then?
> 
> No, it shouldn't depend on any FBDEV stuff since it's not actually
> required. It just happens to help in this case since weston + fbdev
> backend works but not weston with drm backend (or whatever config
> James have set).

I see. Then the correct approach for them would be to just enable CONFIG_FB
and DRM_FBDEV_EMULATION in their kernel config, rather than making this to
depend on anything FB related as you said.

> 
>>
>>> I looked some more at the logs and it seems weston doesn't work on his
>>> system without the fbdev backend. So the question is why weston isn't
>>> working without fbdev? Perhaps this is just a Weston configuration
>>> issue?
>>>
>>
>> But is weston using the fbdev emulated by DRM or the one registered by
>> efifb? I thought that the latter from what was mentioned in this thread.
> 
> It's using drm fbdev emulation with gma500 so EFIFB has nothing to do
> with this. I believe it was just simply incorrectly reported. If I'm
> correct then "depends on FB" is what makes video output work for
> James.
> 

Got it. Thanks for the clarification.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat