linux-kernel - Re: [PATCH v2] gpu: nova-core: falcon: align DMA transfers to 256 bytes

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Message-Id: <DC851M0PQQT4.298DSVDC1RKB0@kernel.org>
Date: Thu, 21 Aug 2025 15:26:02 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Alexandre Courbot" <acourbot@...dia.com>
Cc: "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
 <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gpu: nova-core: falcon: align DMA transfers to 256
 bytes

On Thu Aug 21, 2025 at 6:49 AM CEST, Alexandre Courbot wrote:
> Falcon DMA transfers are done in 256 bytes increments, and the method
> responsible for initiating the transfer checked that the required length
> was indeed a multiple of 256. While correct, this also requires callers
> to specifically account for this limitation of DMA transfers, and we had
> for instance the fwsec code performing a seemingly arbitrary (and
> potentially overflowing) upwards alignment of the DMEM load size to
> match this requirement.
>
> Let's move that alignment into the loading code itself instead: since it
> is working in terms of number of transfers, we can turn this upwards
> alignment into a non-overflowing operation, and check that the requested
> transfer remains into the limits of the DMA object. This also allows us
> to remove a DMA-specific constant in the fwsec code.
>
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>

Applied to nova-next, thanks!