linux-kernel - Re: [PATCH v8 02/20] mailbox: mtk-cmdq: Refine DMA address handling for the command buffer

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Message-ID: <bd9a2670-008a-4e0a-9ad2-90bdad22778d@collabora.com>
Date: Mon, 20 Oct 2025 12:04:44 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Jason-JH Lin <jason-jh.lin@...iatek.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Jassi Brar <jassisinghbrar@...il.com>,
 Chun-Kuang Hu <chunkuang.hu@...nel.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Matthias Brugger <matthias.bgg@...il.com>,
 Nicolas Dufresne <nicolas@...fresne.ca>, Nancy Lin <nancy.lin@...iatek.com>,
 Singo Chang <singo.chang@...iatek.com>,
 Paul-PL Chen <paul-pl.chen@...iatek.com>, Moudy Ho <moudy.ho@...iatek.com>,
 Xiandong Wang <xiandong.wang@...iatek.com>,
 Sirius Wang <sirius.wang@...iatek.com>, Fei Shao <fshao@...omium.org>,
 Chen-yu Tsai <wenst@...omium.org>,
 Project_Global_Chrome_Upstream_Group@...iatek.com,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [PATCH v8 02/20] mailbox: mtk-cmdq: Refine DMA address handling
 for the command buffer

Il 17/10/25 08:44, Jason-JH Lin ha scritto:
> GCE can only fetch the command buffer address from a 32-bit register.
> Some SoCs support a 35-bit command buffer address for GCE, which
> requires a right shift of 3 bits before setting the address into
> the 32-bit register. A comment has been added to the header of
> cmdq_get_shift_pa() to explain this requirement.
> 
> To prevent the GCE command buffer address from being DMA mapped beyond
> its supported bit range, the DMA bit mask for the device is set during
> initialization.
> 
> Additionally, to ensure the correct shift is applied when setting or
> reading the register that stores the GCE command buffer address,
> new APIs, cmdq_convert_gce_addr() and cmdq_revert_gce_addr(), have
> been introduced for consistent operations on this register.
> 
> The variable type for the command buffer address has been standardized
> to dma_addr_t to prevent handling issues caused by type mismatches.
> 
> Fixes: 0858fde496f8 ("mailbox: cmdq: variablize address shift in platform")
> Signed-off-by: Jason-JH Lin <jason-jh.lin@...iatek.com>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>