[PATCH] drm/fb-helper: Scale back depth to supported maximum

[Ville Syrjälä]

On Fri, Feb 02, 2018 at 02:56:30PM +0100, Linus Walleij wrote:
> On Thu, Feb 1, 2018 at 2:19 PM, Ville Syrjälä
> <ville.syrjala at linux.intel.com> wrote:
> > [Me]
> >> +     /*
> >> +      * If we run into a situation where, for example, the primary plane
> >> +      * supports RGBA5551 (16 bpp, depth 15) but not RGB565 (16 bpp, depth
> >> +      * 16) we need to scale down the depth of the sizes we request.
> >> +      */
> >> +     drm_for_each_plane(plane, fb_helper->dev) {
> >> +             /* Only check the primary plane */
> >> +             if (plane->type != DRM_PLANE_TYPE_PRIMARY)
> >> +                     continue;
> >
> > I think this should look at crtc->primary for each of the crtcs managed
> > by the fb_helper.
> >
> > Also this probably shouldn't look at YUV formats at all?
> 
> I guess I can look into doing it this way, sorry for not knowing how to
> properly inspect DRM objects, I'm lost sometimes...
> 
> > I do wonder if instead we should just have the driver specify the
> > pixel format explicitly instead of trying to guess based on bpp?
> 
> That makes a lot more sense to me actually. It would
> give a better sense of control so the driver feel it knows
> what is actually going on.
> 
> So I would just update
> drm_fb_cma_fbdev_init() and drm_fb_helper_initial_config()
> to pass a reasonable pixel format instead and refactor all the
> way down?

Yeah, something along those lines would seem like the better approach
to me. But it's been a while since I've looked at this code so I might
be totally wrong :)

> 
> It does hit a lot of code on the way, but if everyone thinks this
> is a good idea I can very well take a stab at it.
> 
> Yours,
> Linus Walleij

-- 
Ville Syrjälä
Intel OTC