linux-kernel - Re: [PATCH 1/4] gpu: nova-core: gsp: fix incorrect advancing of write pointer

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Message-Id: <DFY803SR0JSR.3U1NXL7KHCGU1@nvidia.com>
Date: Mon, 26 Jan 2026 13:02:22 +0900
From: "Eliot Courtney" <ecourtney@...dia.com>
To: "Gary Guo" <gary@...yguo.net>, "Eliot Courtney" <ecourtney@...dia.com>,
 "Danilo Krummrich" <dakr@...nel.org>, "Alexandre Courbot"
 <acourbot@...dia.com>, "Alice Ryhl" <aliceryhl@...gle.com>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Alistair Popple"
 <apopple@...dia.com>
Cc: <nouveau@...ts.freedesktop.org>, <rust-for-linux@...r.kernel.org>,
 <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] gpu: nova-core: gsp: fix incorrect advancing of
 write pointer

On Sat Jan 24, 2026 at 3:28 AM JST, Gary Guo wrote:
>> -        let wptr = self.cpu_write_ptr().wrapping_add(elem_count) & MSGQ_NUM_PAGES;
>> +        let wptr = self.cpu_write_ptr().wrapping_add(elem_count) % MSGQ_NUM_PAGES;
>
> So the actual number of pages is indeed 0x3F, not 0x40? That's interesting...

Yes, that's right. I thought it was weird as well, but the reason is
that the first page stores the rx/tx pointers (see `Msgq`) and the
remaining 63 are used for the actual ring buffer.