linux-kernel - Re: [PATCH v3 01/13] gpu: nova-core: Set correct DMA mask

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Message-ID: <94bbd268-efbe-4ff6-ba09-e6254709d981@kernel.org>
Date: Tue, 30 Sep 2025 15:29:41 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alistair Popple <apopple@...dia.com>
Cc: rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 acourbot@...dia.com, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>, 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>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 John Hubbard <jhubbard@...dia.com>, Joel Fernandes <joelagnelf@...dia.com>,
 Timur Tabi <ttabi@...dia.com>, linux-kernel@...r.kernel.org,
 nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v3 01/13] gpu: nova-core: Set correct DMA mask

On 9/30/25 3:16 PM, Alistair Popple wrote:
> +        // SAFETY: No DMA allocations have been made yet
> +        unsafe { pdev.dma_set_mask_and_coherent(DmaMask::new::<47>())? };

I think you forgot to derive the value from the relevant sources, i.e. physical
bus, DMA controller and MMU capabilities.

I assume not all GPU architectures / generations have the exact same capabilities?