[PATCH v3] drm/fourcc: document modifier uniqueness requirements

[Simon Ser]

On Thursday, May 28, 2020 5:49 PM, Marek Olšák <maraeo at gmail.com> wrote:

> On most hardware, there is a minimum pitch alignment for linear and
> any greater multiple of the alignment is fine.
>
> On Navi, the pitch in bytes for linear must be
> align(width * bpp / 8, 256). That's because the hw computes the pitch
> from the width and doesn't allow setting a custom pitch. For that
> reason, multi-GPU sharing might not be possible if the other GPU
> doesn't align the pitch in exactly the same way.

OK. In this case I think it's fine to make the DMA-BUF import fail, as
we've suggested on IRC. The more-or-less planned fix for these buffer
sharing issues is to revive the buffer constraints proposal from the
allocator project. It's a lot of work though.