linux-kernel - Re: [PATCH 0/3] drm/nouveau: Advertise correct modifiers on GB20x

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Message-ID: <CAOFGe972S7S23LGKxEmVq_beyRMpDJE-2rMt0aobPj4HnmWSXw@mail.gmail.com>
Date: Fri, 22 Aug 2025 16:44:11 -0400
From: Faith Ekstrand <faith@...strand.net>
To: James Jones <jajones@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Lyude Paul <lyude@...hat.com>, 
	Faith Ekstrand <faith.ekstrand@...labora.com>, nouveau@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Joel Fernandes <joelagnelf@...dia.com>
Subject: Re: [PATCH 0/3] drm/nouveau: Advertise correct modifiers on GB20x

On Mon, Aug 11, 2025 at 5:57 PM James Jones <jajones@...dia.com> wrote:
>
> This series adds new format modifiers for 8 and 16-bit formats on GB20x
> GPUs, preventing them from mistakenly sharing block-linear surfaces
> using these formats with prior GPUs that use a different layout.
>
> There are a few ways the parameteric format modifier definition
> could have been altered to handle the new layouts:
>
> -The GOB Height and Page Kind field has a reserved value that could
>  have been used. However, the GOB height and page kind enums did
>  not change relative to prior chips, so this is sort of a lie.
>  However, this is the least-invasive change.
>
> -An entirely new field could have been added. This seems
>  inappropriate given the presence of an existing appropriate field.
>  The advantage here is it avoids splitting the sector layout field
>  across two bitfields.
>
> The chosen approach is the logically consistent one, but has the
> downside of being the most complex, and that it causes the
> DRM_FORMAT_MOD_NVIDIA_BLOCK_LINEAR_2D() macro to evaluate its 's'
> parameter twice. However, utilizing simple helper functions in
> client code when accessing the parameteric format modifier fields
> easily addresses the complexity, and I have audited the relevant code
> and do not believe the double evaluation should cause any problems in
> practice.
>
> Tested on GB20x and TU10x cards using the following:
>
> -kmscube w/NVK+Zink built with these patches applied:
>
>    https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36336

Both the Mesa and kernel pieces are now reviewed so I think we're good
to start landing. I've independently tested with kmscube to verify.

~Faith

>
>  with various manually specified formats
>  and both manually specified and automatically
>  selected modifiers.
>
> -drmfmtmods, a tiny test program that lists modifiers:
>
>    https://github.com/cubanismo/drmfmtmods
>
> Changes since the RFC version here:
>
>   https://lore.kernel.org/nouveau/20250703223658.1457-1-jajones@nvidia.com/
>
> -Dropped the helper macros & static inlines in
>  drm_fourcc.h as requested by Faith Ekstrand,
>  who noted these aren't helpful for UMD code,
>  which is all written in rust now. I may re-
>  introduce some of these in a subsequent series,
>  but we both agreed we do not want to delay
>  progress on the modifiers themselves while we
>  debate the details of those cometic details.
>
> -Reserved an extra bit for future sector
>  layouts.
>
> -Fixed handling of linear modifiers on GB20x
>  and NV5x/G8x/G9x/GT2xx chips.
>
> James Jones (3):
>   drm: define NVIDIA DRM format modifiers for GB20x
>   drm/nouveau/disp: Always accept linear modifier
>   drm/nouveau: Advertise correct modifiers on GB20x
>
>  drivers/gpu/drm/nouveau/dispnv50/disp.c     |  3 ++
>  drivers/gpu/drm/nouveau/dispnv50/disp.h     |  1 +
>  drivers/gpu/drm/nouveau/dispnv50/wndw.c     | 25 ++++++++++++++--
>  drivers/gpu/drm/nouveau/dispnv50/wndwca7e.c | 33 +++++++++++++++++++++
>  include/uapi/drm/drm_fourcc.h               | 25 ++++++++++------
>  5 files changed, 76 insertions(+), 11 deletions(-)
>
> --
> 2.50.1
>