Re: [PATCH] drm/fourcc: add LINEAR modifiers with an exact pitch alignment

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Jan 20, 2025 at 08:58:20AM +0100, Thomas Zimmermann wrote:
> Am 18.01.25 um 03:37 schrieb Marek Olšák:
> [...]
> >
> > 3) Implementing DRM_FORMAT_MOD_LINEAR as having 256B pitch and offset 
> > alignment. This is what we do today. Even if Intel and some AMD chips 
> > can do 64B or 128B alignment, they overalign to 256B. With so many 
> > AMD+NV laptops out there, NV is probably next, unless they already do 
> > this in the closed source driver.
> 
> The dumb-buffer series currently being discussed on dri-devel also 
> touches handling of scanline pitches. THe actual value varies with each 
> driver.  Should dumb buffers use a default pitch alignment of 256 on al 
> hardware?

That may break sharing buffers with other devices (codecs, NPUs and/or
cameras) that would not support a configurable pitch. I don't expect
that to be the majority case, but I can't rule it out either. There's
also the issue that, even if the devices support configurable pitches,
the drivers may not implement it. That's fixable, but hardcoding the
pitch to 256 bytes without fixing that would be a regression.

-- 
Regards,

Laurent Pinchart