linux-kernel - Re: [PATCH v2 4/9] dt-bindings: dma: stm32-dma3: prevent additional transfers

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Message-ID: <20241015213053.GA1992090-robh@kernel.org>
Date: Tue, 15 Oct 2024 16:30:53 -0500
From: Rob Herring <robh@...nel.org>
To: Amelie Delaunay <amelie.delaunay@...s.st.com>
Cc: Vinod Koul <vkoul@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	dmaengine@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/9] dt-bindings: dma: stm32-dma3: prevent additional
 transfers

On Tue, Oct 15, 2024 at 02:14:40PM +0200, Amelie Delaunay wrote:
> stm32-dma3 driver refactors the linked-list in order to address the memory
> with the highest possible data width.

You are still talking about driver...

> It means that it can introduce up to 2 linked-list items. One with a
> transfer length multiple of channel maximum burst length and so with the
> highest possible data width. And an extra one with the latest bytes, with
> lower data width.
> Some devices (e.g. FMC ECC) don't support having several transfers instead
> of only one.
> So add the possibility to prevent these additional transfers, by setting
> bit 17 of the 'DMA transfer requirements' bit mask.

Some devices require single transfers. That's about all you need to say.

> 
> Signed-off-by: Amelie Delaunay <amelie.delaunay@...s.st.com>
> ---
> Changes in v2:
> - Reword commit title/message/content as per Rob's suggestion.
> ---
>  Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> index 5484848735f8ac3d2050104bbab1d986e82ba6a7..36f9fe860eb990e6caccedd31460ee6993772a35 100644
> --- a/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> +++ b/Documentation/devicetree/bindings/dma/stm32/st,stm32-dma3.yaml
> @@ -99,6 +99,9 @@ properties:
>          -bit 16: Prevent packing/unpacking mode
>            0x0: pack/unpack enabled when source data width/burst != destination data width/burst
>            0x1: memory data width/burst forced to peripheral data width/burst to prevent pack/unpack
> +        -bit 17: Prevent additional transfers due to linked-list refactoring
> +          0x0: don't prevent additional transfers for optimal performance
> +          0x1: prevent additional transfer to accommodate user constraints such as single transfer
>  
>  required:
>    - compatible
> 
> -- 
> 2.25.1
>