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Mon, 02 Nov 2026 12:38:21 -0800 (PST) Received: from [10.67.48.245] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-91ca7f26f1esm100674086d6.13.2026.11.02.12.38.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Nov 2026 12:38:20 -0800 (PST) Message-ID: <5bd67c8d-41ee-40e7-ab75-031e1520758f@gmail.com> Date: Mon, 2 Nov 2026 12:38:15 -0800 X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/9] dt-bindings: dma: brcm,bcm2835-dma: Add BCM2711 and BCM2712 To: Peter Robinson , Conor Dooley Cc: Florian Fainelli , Dave Stevenson , Ray Jui , Scott Branden , Vinod Koul , Frank Li , dmaengine@vger.kernel.org, devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, bcm-kernel-feedback-list@broadcom.com, Rob Herring , Krzysztof Kozlowski , Conor Dooley References: <20261102090713.896324-1-pbrobinson@gmail.com> <20261102090713.896324-2-pbrobinson@gmail.com> <20261102-email-target-d3191584d234@spud> Content-Language: en-US, fr-FR From: Florian Fainelli In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/2/26 12:18, Peter Robinson wrote: > On Mon, 2 Nov 2026 at 19:39, Conor Dooley wrote: >> >> On Mon, Nov 02, 2026 at 09:06:51AM +0000, Peter Robinson wrote: >>> Add compatibles for the BCM2711 40-bit DMA4 channels, which are >>> described by a separate node covering channels 11-14, and for the >>> BCM2712 DMA controllers. The register address of a node identifies its >>> first channel, allowing a controller to be split across nodes. >>> >>> Signed-off-by: Peter Robinson >>> Cc: Rob Herring >>> Cc: Krzysztof Kozlowski >>> Cc: Conor Dooley >>> >>> --- >>> .../bindings/dma/brcm,bcm2835-dma.yaml | 31 +++++++++++++++++-- >>> 1 file changed, 29 insertions(+), 2 deletions(-) >>> >>> diff --git a/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml b/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml >>> index c9b9a5490826c..31d97a10a0ea9 100644 >>> --- a/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml >>> +++ b/Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml >>> @@ -9,18 +9,27 @@ title: BCM2835 DMA controller >>> maintainers: >>> - Nicolas Saenz Julienne >>> >>> -description: >>> +description: | >>> The BCM2835 DMA controller has 16 channels in total. Only the lower >>> 13 channels have an associated IRQ. Some arbitrary channels are used by the >>> VideoCore firmware (1,3,6,7 in the current firmware version). The channels >>> 0, 2 and 3 have special functionality and should not be used by the driver. >>> >>> + BCM2711 channels 11 to 14 are 40-bit capable DMA4 channels, described by a >>> + separate brcm,bcm2711-dma node. BCM2712 has 40-bit addressing on all >>> + channels, with channels 6 to 11 being DMA4 channels. A controller may be >>> + split across several nodes, the register address identifies the first >>> + channel of a node. >> >> Uh no, a device should not be split across different nodes. This should >> not be needed, why can't your driver handle the upper channels having >> different capabilities? > > This is the way it's done in the downstream kernel, unfortunately > Broadcom doesn't publish the HW details so either they'd need to > contribute the support (which they've not done since the RPi4 was > available) or I'm not sure what the other options would be. Open to > suggestions. Neither here nor there, IMHO, yes it would be nice if documentation was published (and a customer like Raspberry Pi is probably one of the few that can get the needle to move there). You have the bcm2711 and bcm2712 compatible strings which should be enough for you to know which channels are 40-bit capable and which are not, yet keep the same Device Tree node. -- Florian