Re: [PATCH v2 25/25] drm/xlnx: Compute dumb-buffer sizes with drm_mode_size_dumb()

[Daniel Stone <daniel@xxxxxxxxxxxxx>]

On Wed, 15 Jan 2025 at 14:20, Tomi Valkeinen
<tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
> No disagreement there, we need CREATE_DUMB2.
>
> My point is that we have the current UAPI, and we have userspace using
> it, but we don't have clear rules what the ioctl does with specific
> parameters, and we don't document how it has to be used.
>
> Perhaps the situation is bad, and all we can really say is that
> CREATE_DUMB only works for use with simple RGB formats, and the behavior
> for all other formats is platform specific. But I think even that would
> be valuable in the UAPI docs.

Yeah, CREATE_DUMB only works for use with simple RGB formats in a
linear layout. Not monochrome or YUV or tiled or displayed rotated or
whatever.

If it happens to accidentally work for other uses, that's fine, but
it's not generically reliable for anything other than simple linear
RGB. It's intended to let you do splash screens, consoles, recovery
password entries, and software-rendered compositors if you really
want. Anything more than that isn't 'dumb'.

Cheers,
Daniel