linux-kernel - Re: [PATCH 2/4] drm/gpuvm: drm_gpuvm_bo_obtain() requires lock and staged mode

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Message-Id: <DF26WBIDPMPU.3E6XTUPMZTHW1@kernel.org>
Date: Fri, 19 Dec 2025 13:25:05 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Daniel Almeida" <daniel.almeida@...labora.com>, "Matthew Brost"
 <matthew.brost@...el.com>, Thomas Hellström
 <thomas.hellstrom@...ux.intel.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Boris Brezillon"
 <boris.brezillon@...labora.com>, "Steven Price" <steven.price@....com>,
 "Liviu Dudau" <liviu.dudau@....com>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Trevor
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 Coster" <matt.coster@...tec.com>, "Rob Clark"
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 "Abhinav Kumar" <abhinav.kumar@...ux.dev>, "Jessica Zhang"
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 Suijten" <marijn.suijten@...ainline.org>, "Lyude Paul" <lyude@...hat.com>,
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 <rodrigo.vivi@...el.com>, "Sumit Semwal" <sumit.semwal@...aro.org>,
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Subject: Re: [PATCH 2/4] drm/gpuvm: drm_gpuvm_bo_obtain() requires lock and
 staged mode

On Fri Nov 28, 2025 at 3:14 PM CET, Alice Ryhl wrote:
> In the previous commit we updated drm_gpuvm_bo_obtain_prealloc() to take
> locks internally, which means that it's only usable in immediate mode.
> In this commit, we notice that drm_gpuvm_bo_obtain() requires you to use
> staged mode. This means that we now have one variant of obtain for each
> mode you might use gpuvm in.
>
> To reflect this information, we add a warning about using it in
> immediate mode, and to make the distinction clearer we rename the method
> with a _locked() suffix so that it's clear that it requires the caller
> to take the locks.
>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

Ultimately, the two different approaches of obtaining a VM_BO have always been
desinged for the two different modes of operation -- great to see this refined!

Given that, I think it would be great to update the "Locking" section of the
GPUVM's documentation and expand it with a new section "Modes of Operation".

Mind sending a follow-up patch / series for this?