[PATCH 1/2] drm: Add new DRM_IOCTL_MODE_GETPLANE2

[Rob Clark]

On Tue, Dec 20, 2016 at 7:12 PM, Kristian H. Kristensen
<hoegsberg at gmail.com> wrote:
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index ce7efe2..cea3de3 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -209,6 +209,33 @@ struct drm_mode_get_plane {
>         __u64 format_type_ptr;
>  };
>
> +struct drm_format_modifier {
> +       /* Bitmask of formats in get_plane format list this info
> +        * applies to. */
> +       uint64_t formats;

Hmm, this seems a bit clunky/brittle when you have a lot of supported
formats (esp. if format order changes or new formats are not added at
end).  I guess fine when you support a four or five different formats,
but I think you'll start to hate maintaining those tables on hw that
supports more.

Also I guess it limits you to modifiers only with the first 64
formats.. maybe not a problem right away, but a quick look and drm/msm
is already at 23 formats (and there are probably some more it could
do.. without even starting to get into "exotic" float/etc formats and
whatever else might come in the future.

Not that I really have a better idea..  maybe just instead of
getplane2 we just add a querymodifiers ioctl (ie. fourcc in, list of
modifiers out), with the idea that userspace probably knows what
format/fourcc it wants to use, and only just cares about modifiers for
that particular fourcc..

BR,
-R

> +       /* This modifier can be used with the format for this plane. */
> +       uint64_t modifier;
> +};
> +