linux-kernel - Re: [PATCH 1/3] drm: define NVIDIA DRM format modifiers for GB20x

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Message-ID: <1cbcceed-6e95-4f20-8666-1c8f40154e3b@kernel.org>
Date: Tue, 2 Sep 2025 15:41:16 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: James Jones <jajones@...dia.com>
Cc: 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 1/3] drm: define NVIDIA DRM format modifiers for GB20x

On 8/12/25 12:00 AM, James Jones wrote:
> The layout of bits within the individual tiles
> (referred to as sectors in the
> DRM_FORMAT_MOD_NVIDIA_BLOCK_LINEAR_2D() macro)
> changed for 8 and 16-bit surfaces starting in
> Blackwell 2 GPUs (With the exception of GB10).
> To denote the difference, extend the sector field
> in the parametric format modifier definition used
> to generate modifier values for NVIDIA hardware.
> 
> Without this change, it would be impossible to
> differentiate the two layouts based on modifiers,
> and as a result software could attempt to share
> surfaces directly between pre-GB20x and GB20x
> cards, resulting in corruption when the surface
> was accessed on one of the GPUs after being
> populated with content by the other.
> 
> Of note: This change causes the
> DRM_FORMAT_MOD_NVIDIA_BLOCK_LINEAR_2D() macro to
> evaluate its "s" parameter twice, with the side
> effects that entails. I surveyed all usage of the
> modifier in the kernel and Mesa code, and that
> does not appear to be problematic in any current
> usage, but I thought it was worth calling out.
> 
> Signed-off-by: James Jones <jajones@...dia.com>

Having a second look on this, isn't this (and patch 3) a fix as well?