[PATCH] drm: Don't create the IN_FORMATS blob when the driver does not provide .format_mod_supported()

[Daniel Vetter]

On Sat, Oct 24, 2020 at 12:52 AM Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
>
> On Fri, Oct 23, 2020 at 10:03:50PM +0000, Simon Ser wrote:
> > On Friday, October 23, 2020 10:39 PM, Ville Syrjala <ville.syrjala at linux.intel.com> wrote:
> >
> > > From: Ville Syrjälä ville.syrjala at linux.intel.com
> > >
> > > The code responsible for creating the IN_FORMATS
> > > blob is broken when the driver doesn't provide a
> > > .format_mod_supported() hook. It just copies in
> > > the format list, but leaves all the modifier information
> > > zeroed. That would indicate (in a very silly way) that
> > > there are in fact no supported format+modifier combinations.
> > > That is utter nonsense.
> >
> > Should we WARN_ON when the driver enables allow_fb_modifiers but
> > doesn't populate format_mod_supported?
>
> .format_mod_supported() was supposed to be optional IIRC.
>
> But now that I look at it, it looks like only these
> drivers are lacking .format_mod_supported(): exynos, mxsfb,
> tiny/cirrus, tiny/gm12u320.
>
> There is some other oddity going on with sun4i which sometimes
> uses modifiers sometimes it doesn't. No idea what is going on there.
> But it does have .format_mod_supported() at least.
>
> So I guess if we can get exynos, mxsfb, and tiny/* to implement
> the hook then we could make it mandatory.

I'd just delete it all, since it's obviously not tested for these
drivers. And then add a patch which warns if allow_fb_modifiers,
modifiers list passed y/n and .format_mod_support don't all agree.
Since a bunch of your don't even set allow_fb_modifiers but pass a
format list. So it's a complete mess :-/

Next step would then be to add some todo items, at least the
simple/tiny drivers should all be able to do this fairly easily, and
probably with linear only as the default.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch