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Date: Sun, 05 Apr 2026 17:15:44 +0200
Message-Id: <DHLBJ9NMLXFB.5H53BZ132FHG@kernel.org>
Subject: Re: [PATCH v2] gpu: nova-core: falcon: pad firmware DMA object size
 to required block alignment
Cc: "Alice Ryhl" <aliceryhl@google.com>, "David Airlie" <airlied@gmail.com>,
 "Simona Vetter" <simona@ffwll.ch>, "Gary Guo" <gary@garyguo.net>, "John
 Hubbard" <jhubbard@nvidia.com>, "Alistair Popple" <apopple@nvidia.com>,
 "Joel Fernandes" <joelagnelf@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 "Zhi Wang" <zhiw@nvidia.com>, "Eliot Courtney" <ecourtney@nvidia.com>,
 <dri-devel@lists.freedesktop.org>, <rust-for-linux@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
To: "Alexandre Courbot" <acourbot@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260405-falcon-dma-roundup-v2-1-4af5b2ff9c16@nvidia.com>
In-Reply-To: <20260405-falcon-dma-roundup-v2-1-4af5b2ff9c16@nvidia.com>

On Sun Apr 5, 2026 at 4:22 AM CEST, Alexandre Courbot wrote:
> Commit a88831502c8f ("gpu: nova-core: falcon: use dma::Coherent")
> dropped the nova-local `DmaObject` device memory type for the
> kernel-global `Coherent` one.
>
> This switch had a side-effect: `DmaObject` always aligned the requested
> size to `PAGE_SIZE`, and also reported that adjusted size when queried.
> `Coherent`, on the other hand, does page-align allocation sizes but only
> allows CPU access on the exact size provided by the caller.
>
> This change runs into a limitation of falcon DMA copies, namely that DMA
> accesses are done on blocks of exactly 256 bytes. If the provided data
> does not have a length that is a multiple of 256, `dma_wr` returns
> an error.
>
> It was expected that all firmwares would present the proper adjusted
> size, but this is not the case at least on my GA107:
>
>     NovaCore 0000:08:00.0: DMA transfer goes beyond range of DMA object
>     NovaCore 0000:08:00.0: Failed to load FWSEC firmware: EINVAL
>     NovaCore 0000:08:00.0: probe with driver NovaCore failed with error -=
22
>
> Fix this by padding the `Coherent`'s size to `MEM_BLOCK_ALIGNMENT` (i.e.
> 256) when allocating it and filling it with zeroes, before copying the
> firmware on top of it.
>
> Fixes: a88831502c8f ("gpu: nova-core: falcon: use dma::Coherent")
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

Applied to drm-rust-next, thanks!