[PATCH v2 09/15] drm/fbconv: Mode-setting pipeline enable / disable

[Geert Uytterhoeven]

Hi Thomas,

On Mon, May 30, 2022 at 10:34 AM Geert Uytterhoeven
<geert at linux-m68k.org> wrote:
> On Mon, May 30, 2022 at 9:47 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
> > Am 28.05.22 um 22:17 schrieb Geert Uytterhoeven:
> > > On Mon, Oct 14, 2019 at 4:05 PM Thomas Zimmermann <tzimmermann at suse.de> wrote:
> > >> The display mode is set by converting the DRM display mode to an
> > >> fb_info state and handling it to the fbdev driver's fb_setvar()
> > >> function. This also requires a color depth, which we take from the
> > >> value of struct drm_mode_config.preferred_depth
> > >>
> > >> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> > >
> > >> --- a/drivers/gpu/drm/drm_fbconv_helper.c
> > >> +++ b/drivers/gpu/drm/drm_fbconv_helper.c
> > >> @@ -919,6 +919,24 @@ static int drm_fbconv_update_fb_var_screeninfo_from_framebuffer(
> > >>          return 0;
> > >>   }
> > >>
> > >> +static int drm_fbconv_update_fb_var_screeninfo_from_simple_display_pipe(
> > >> +       struct fb_var_screeninfo *fb_var, struct drm_simple_display_pipe *pipe)
> > >> +{
> > >> +       struct drm_plane *primary = pipe->crtc.primary;
> > >> +       struct drm_fbconv_modeset *modeset = drm_fbconv_modeset_of_pipe(pipe);
> > >> +
> > >> +       if (primary && primary->state && primary->state->fb)
> > >> +               return drm_fbconv_update_fb_var_screeninfo_from_framebuffer(
> > >> +                       fb_var, primary->state->fb,
> > >> +                       modeset->fb_info->fix.smem_len);
> > >> +
> > >> +       fb_var->xres_virtual = fb_var->xres;
> > >> +       fb_var->yres_virtual = fb_var->yres;
> > >> +       fb_var->bits_per_pixel = modeset->dev->mode_config.preferred_depth;
> > >
> > > This looks wrong to me: IMHO bits_per_pixel should be derived from
> > > the fourcc format of the _new_ mode to be set...
> >
> > Indeed, this appears to be wrong.
>
> OK.
>
> >
> > >
> > >> +
> > >> +       return 0;
> > >> +}
> > >> +
> > >>   /**
> > >>    * drm_fbconv_simple_display_pipe_mode_valid - default implementation for
> > >>    *     struct drm_simple_display_pipe_funcs.mode_valid
> > >> @@ -950,6 +968,28 @@ bool drm_fbconv_simple_display_pipe_mode_fixup(
> > >>          struct drm_crtc *crtc, const struct drm_display_mode *mode,
> > >>          struct drm_display_mode *adjusted_mode)
> > >>   {
> > >> +       struct drm_simple_display_pipe *pipe =
> > >> +               container_of(crtc, struct drm_simple_display_pipe, crtc);
> > >> +       struct drm_fbconv_modeset *modeset = drm_fbconv_modeset_of_pipe(pipe);
> > >> +       struct fb_var_screeninfo fb_var;
> > >> +       int ret;
> > >> +
> > >> +       if (!modeset->fb_info->fbops->fb_check_var)
> > >> +               return true;
> > >> +
> > >> +       drm_fbconv_init_fb_var_screeninfo_from_mode(&fb_var, mode);
> > >> +
> > >> +       ret = drm_fbconv_update_fb_var_screeninfo_from_simple_display_pipe(
> > >> +               &fb_var, &modeset->pipe);
> > >> +       if (ret)
> > >> +               return true;
> > >> +
> > >> +       ret = modeset->fb_info->fbops->fb_check_var(&fb_var, modeset->fb_info);
> > >
> > > ... hence this fails if the requested mode is valid with the new
> > > fourcc format, but invalid with the old (but preferred) depth.
> > > E.g. due to bandwidth limitations, a high-resolution mode is valid
> > > with a low color depth, while a high color depth is limited to lower
> > > resolutions.

> > > Unfortunately we do not know the new fourcc format here, as both
> > > drm_simple_display_pipe_funcs.mode_{valid,fixup}() are passed
> > > the mode (from drm_mode_set.mode), but not the new format (from
> > > drm_mode_set.fb->format).
> > >
> > > Am I missing something? Is the new format available in some other way?
> >
> > We can always get the format from the new plane state of
> > modeset->pipe->plane. We'd have this in the atomic_check call. And it
> > appears that drm_fbconv_simple_display_pipe_check() is a better place
> > for this code anyway.
>
> Thanks, I'll give that a try!

Getting the format from the new plane state of pipe->plane doesn't
work, as pipe->plane.state->fb = NULL.
But it is indeed available in the drm_simple_display_pipe_funcs.check()
callback, so that seems to work...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds