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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Melissa Wen <melissa.srw@gmail.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Haneen Mohammed <hamohammed.sa@gmail.com>
Subject: Re: [PATCH 1/3] drm/vkms: Set preferred depth correctly
Date: Sat, 17 Oct 2020 17:23:06 +0200	[thread overview]
Message-ID: <CAKMK7uFq2kL2Owt_ZtTD6HR5UmpuGUpB+Derumm6v+SinGrsdA@mail.gmail.com> (raw)
In-Reply-To: <20201017083940.xlq6g3visn2gojuu@smtp.gmail.com>

On Sat, Oct 17, 2020 at 10:39 AM Melissa Wen <melissa.srw@gmail.com> wrote:
>
> On 10/16, Daniel Vetter wrote:
> > On Fri, Oct 16, 2020 at 7:02 PM Melissa Wen <melissa.srw@gmail.com> wrote:
> > >
> > > On 10/16, Daniel Vetter wrote:
> > > > On Fri, Oct 16, 2020 at 12:38 PM Simon Ser <contact@emersion.fr> wrote:
> > > > >
> > > > > > The only thing we support is xrgb8888.
> > > > > >
> > > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > > > > Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> > > > > > Cc: Melissa Wen <melissa.srw@gmail.com>
> > > > > > Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
> > > > > > Cc: Daniel Vetter <daniel@ffwll.ch>
> > > > > > ---
> > > > > >  drivers/gpu/drm/vkms/vkms_drv.c | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> > > > > > index 726801ab44d4..eb4007443706 100644
> > > > > > --- a/drivers/gpu/drm/vkms/vkms_drv.c
> > > > > > +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> > > > > > @@ -124,7 +124,7 @@ static int vkms_modeset_init(struct vkms_device *vkmsdev)
> > > > > >       dev->mode_config.max_height = YRES_MAX;
> > > > > >       dev->mode_config.cursor_width = 512;
> > > > > >       dev->mode_config.cursor_height = 512;
> > > > > > -     dev->mode_config.preferred_depth = 24;
> > > > > > +     dev->mode_config.preferred_depth = 32;
> > > > >
> > > > > Are you sure xrgb8888's depth is 32 and not 24? Looking at drmdb [1], *all*
> > > > > drivers set it to 24.
> > > >
> > > > Uh there's a problem I think. Depth should indeed stay at 24, the
> > > > problem is that fb helpers directly take that to be the bpp parameter,
> > > > which is a different thing. And if you look at how most drivers set up
> > > > that, they pick 32.
> > > >
> > > > I guess I need to revert this here, and unconfuse the fb helpers about
> > > > depth vs bpp.
> > >
> > > Hi guys,
> > >
> > > Perhaps it deserves to be pointed out: the documentation says
> > > "preferred_depth: preferred RBG(sic) pixel depth, used by fb helpers",
> > > and looking to fb helpers, preferred_depth is only used by
> > > generic_setup, as bits by pixel (if I didn't miss something there).
> > >
> > > In fact, the alpha channel is not used for final display (perhaps in the
> > > future); however, I saw another driver with a change similar to this
> > > here and, possibly like me, following the same misunderstanding.
> >
> > Yeah the problem is that preferred_depth is depth, and that means 24
> > bit for XRGB8888. But bpp as used by fb helpers would be 32 bit for
> > XRGB8888.
> >
> > I think the real fix here is to switch this entire mess over to using
> > drm_fourcc codes directly, at least for atomic drivers. Which nowadays
> > are most. Interim I'm not sure whether we should revert my patch (it
> > breaks fbdev) or switch preferred_depth to 0, which means we get the
> > default every, and that means both fbdev helpers and userspace will
> > pick XRGB8888.
>
> hmm... but why not keep preferred_depth = 24 and pass 32 as the
> preferred_bpp parameter of fbdev_generic_setup?

The goal is to get rid of this parameter in fbdev_generic_setup. It
should be able to figure this out automatically, like any kms client
in userspace.

What does work is setting preferred_bpp = 0. Userspace will pick the
default (which is generally 24 depth, 32bpp), and fbcon do the same.

And then I guess a nice patch series to clean up this mess.
-Daniel

> > -Daniel
> >
> > > Melissa
> > > >
> > > > Maybe best would be to just switch over to preferred drm_fourcc format
> > > > code, or maybe just pick this up from the first format the primary
> > > > plane supports.
> > > >
> > > > This is all getting slightly tricky and a lot more work :-/
> > > > -Daniel
> > > > --
> > > > Daniel Vetter
> > > > Software Engineer, Intel Corporation
> > > > http://blog.ffwll.ch
> >
> >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

  reply	other threads:[~2020-10-17 15:23 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-09 23:21 Daniel Vetter
2020-10-09 23:21 ` [PATCH 2/3] drm/vkms: Switch to shmem helpers Daniel Vetter
2020-10-12 10:59   ` Chris Wilson
2020-10-12 11:20     ` Thomas Zimmermann
2020-10-12 11:22   ` Thomas Zimmermann
2020-10-12 12:41   ` Melissa Wen
2020-10-13 11:10   ` [PATCH] " Daniel Vetter
2020-10-09 23:21 ` [PATCH 3/3] drm/vkms: fbdev emulation support Daniel Vetter
2020-10-12 11:24   ` Thomas Zimmermann
2020-10-12 12:40     ` Neil Armstrong
2020-10-12 14:23       ` Daniel Vetter
2020-10-13  6:14         ` Pekka Paalanen
2020-10-13  7:53           ` Daniel Vetter
2020-10-13 10:19             ` Pekka Paalanen
2020-10-13 11:03               ` Daniel Vetter
2020-10-16 10:10   ` Melissa Wen
2020-10-20  8:34     ` Daniel Vetter
2020-10-12 11:08 ` [PATCH 1/3] drm/vkms: Set preferred depth correctly Thomas Zimmermann
2020-10-12 12:59 ` Melissa Wen
2020-10-15 21:39   ` Daniel Vetter
2020-10-16 10:18     ` Melissa Wen
2020-10-16 10:38 ` Simon Ser
2020-10-16 11:35   ` Daniel Vetter
2020-10-16 17:02     ` Melissa Wen
2020-10-16 17:05       ` Daniel Vetter
2020-10-17  8:39         ` Melissa Wen
2020-10-17 15:23           ` Daniel Vetter [this message]
2020-10-27 10:13     ` Thomas Zimmermann
2020-10-27 10:18       ` Daniel Vetter

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