From: "Alexandre Courbot" <acourbot@nvidia.com>
To: "Eliot Courtney" <ecourtney@nvidia.com>
Cc: "Danilo Krummrich" <dakr@kernel.org>,
"Alice Ryhl" <aliceryhl@google.com>,
"David Airlie" <airlied@gmail.com>,
"Simona Vetter" <simona@ffwll.ch>,
"John Hubbard" <jhubbard@nvidia.com>,
"Alistair Popple" <apopple@nvidia.com>,
"Timur Tabi" <ttabi@nvidia.com>, <nova-gpu@lists.linux.dev>,
<dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] gpu: nova-core: gsp: cmdq: increase MSGQ_NUM_PAGES to 64
Date: Thu, 12 Nov 2026 22:07:06 +0900 [thread overview]
Message-ID: <DMT976BWDM94.111ZSOZDKPBUO@nvidia.com> (raw)
In-Reply-To: <20261112-msgq-64-pages-v2-2-bc1e6f7301ca@nvidia.com>
On Thu Nov 12, 2026 at 3:14 PM JST, Eliot Courtney wrote:
> In the msgq v2 protocol, which the r000 firmware uses, the queue
> pointers are kept in u32 registers and increase monotonically until they
> wrap at 2^32.
>
> `MSGQ_NUM_PAGES` is currently 63 and does not divide 2^32. This means
> that on msgq v2, the slot can jump backwards when the counters wrap.
> For example:
>
> (2^32 - 2) % 63 == 2
> (2^32 - 1) % 63 == 3
> 0 % 63 == 0 (slot 0 instead of slot 4)
>
> The writer can then overwrite slots before the reader has read them.
>
> Increase `MSGQ_NUM_PAGES` to 64 and check at compile time that
> `MSGQ_NUM_PAGES` divides 2^32.
>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
next prev parent reply other threads:[~2026-11-12 13:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-12 6:14 [PATCH v2 0/2] gpu: nova-core: gsp: fix misc cmdq issues Eliot Courtney
2026-11-12 6:14 ` [PATCH v2 1/2] gpu: nova-core: gsp: cmdq: wrap the sequence number on overflow Eliot Courtney
2026-11-12 6:14 ` [PATCH v2 2/2] gpu: nova-core: gsp: cmdq: increase MSGQ_NUM_PAGES to 64 Eliot Courtney
2026-11-12 13:07 ` Alexandre Courbot [this message]
2026-11-12 13:08 ` [PATCH v2 0/2] gpu: nova-core: gsp: fix misc cmdq issues Alexandre Courbot
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