Re: [PATCH v2 2/2] gpu: nova-core: gsp: cmdq: increase MSGQ_NUM_PAGES to 64

[Alexandre Courbot]

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@xxxxxxxxxx>

Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>