Re: [PATCH v2 5/8] drm/client: Convert drm_client_buffer_addfb() to drm_mode_addfb2()

[Thomas Zimmermann]

Hi

Am 24.08.23 um 17:22 schrieb Geert Uytterhoeven:
> Hi Daniel,
>
> On Thu, Aug 24, 2023 at 5:12 PM Daniel Stone <daniel@xxxxxxxxxxxxx> wrote:
> > On Thu, 24 Aug 2023 at 16:09, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > >          struct drm_client_dev *client = buffer->client;
> > > -       struct drm_mode_fb_cmd fb_req = { };
> > > -       const struct drm_format_info *info;
> > > +       struct drm_mode_fb_cmd2 fb_req = { };
> > >          int ret;
> > >
> > > -       info = drm_format_info(format);
> > > -       fb_req.bpp = drm_format_info_bpp(info, 0);
> > > -       fb_req.depth = info->depth;
> > >          fb_req.width = width;
> > >          fb_req.height = height;
> > > -       fb_req.handle = handle;
> > > -       fb_req.pitch = buffer->pitch;
> > > +       fb_req.pixel_format = format;
> > > +       fb_req.handles[0] = handle;
> > > +       fb_req.pitches[0] = buffer->pitch;
> > >
> > > -       ret = drm_mode_addfb(client->dev, &fb_req, client->file);
> > > +       ret = drm_mode_addfb2(client->dev, &fb_req, client->file);
> > >          if (ret)
> > >                  return ret;
> >
> > This should explicitly set the LINEAR modifier (and the modifier flag)
> > if the driver supports modifiers.
>
> Thanks for your comment!
>
> I have no idea how to do that, and I do not know what the impact
> would be.  All I know is that the current implementation of
> drm_client_buffer_addfb() does not do that, so changing that in this
> patch would mean that this would no longer be a trivial conversion.

I agree. That change is too large and invasive for this patchset. Rather 
add a comment or TODO item.

The correct way for adding the modifier is to extend the 
drm_client_buffer_addfb() and pass in the information from the caller. 
That caller is fbdev code. We currently detect the format from (bpp, 
depth) values and forward the format to _addfb(). [1] Here we'd have to 
check the driver for a modifier as well and forward it to _addfb()

[1] 
https://elixir.bootlin.com/linux/v6.5/source/drivers/gpu/drm/drm_fbdev_generic.c#L88

The pair of (bpp, depth) values comes from __drm_fb_helper_find_sizes, 
[2] which looks through the planes' formats and tries to find something 
that fits the user's requested color mode. It would have to look for 
modifiers as well. At some point, I want the helper to return formats 
directly, but that's still a bit away.

[2] 
https://elixir.bootlin.com/linux/v6.5/source/drivers/gpu/drm/drm_fb_helper.c#L1504

Best regards
Thomas

> Gr{oetje,eeting}s,
>
>                          Geert

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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