[RFC] drm: add support for tiled/compressed/etc modifier in addfb2

[Rob Clark]

On Thu, Dec 18, 2014 at 4:22 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>> > > > > TODO move definition of tokens to drm_fourcc.h?
>> > > >
>> > > > Seems orthogonal imo. Another todo is to add checking to all drivers to
>> > > > reject it if it's not 0 with -EINVAL. Otherwise we have yet another case
>> > > > of an ioctl with fields that can't actually be used everywhere.
>> > >
>> > > Could we please add the check in core code instead of drivers ?
>> >
>> > Nope since then no driver could ever use that extension. Defeats the point
>> > ;-)
>>
>> Except if we follow the proposal of adding a flag to tell whether a driver
>> supports the extension ;-)
>
> I'm not a terrible big fan of driver flags, mostly because I've seen too
> much of the horrible stuff in dri1. Imo much better to pass everything to
> drivers and help them out with helpers if needed. I might be going
> overboard a bit with my bias against driver flags ;-)

I ventured a little ways down the thought path of adding list of
supported modifier tokens per plane.. and then doing more complete
checks in the core.  But then the question is, what about cases where
some tiling format is only supported for UV but not Y, etc.. it
quickly gets ugly.  I think for now better to let the driver do this
(with a must_be_all_zeros() helper for what I expect will be the
common case initially).  If common patterns emerge, then we refactor
out a better helper..

BR,
-R