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

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Message-ID: <CAMeQTsYYpw5+uLgmDrbB6PUBotRC4F+_rfK+sxT0CpPHoiOmmw@mail.gmail.com>
Date:   Thu, 21 Apr 2022 14:54:37 +0200
From:   Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:     Javier Martinez Canillas <javierm@...hat.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 Thu, Apr 21, 2022 at 2:47 PM Javier Martinez Canillas
<javierm@...hat.com> wrote:
>
> Hello Patrik,
>
> On 4/21/22 14:39, Patrik Jakobsson wrote:
> > On Thu, Apr 21, 2022 at 1:49 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
> >>
> >> Hi
> >>
> >> Am 09.04.22 um 06:23 schrieb James Hilliard:
> >>> Select the efi framebuffer if efi is enabled.
> >>>
> >>> This appears to be needed for video output to function correctly.
> >>>
> >>> Signed-off-by: James Hilliard <james.hilliard1@...il.com>
> >>> ---
> >>> Changes v2 -> v3:
> >>>    - select EFI_FB instead of depending on it
> >>> Changes v1 -> v2:
> >>>    - use depends instead of select
> >>> ---
> >>>   drivers/gpu/drm/gma500/Kconfig | 2 ++
> >>>   1 file changed, 2 insertions(+)
> >>>
> >>> 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 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.

>
> --
> Best regards,
>
> Javier Martinez Canillas
> Linux Engineering
> Red Hat
>