linux-kernel - Re: [PATCH 04/11] dt-bindings: dma: stm32-dma3: prevent linked-list refactoring

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Message-ID: <3b7b46ca-426c-44a9-b4f2-ce104e0d3b1c@foss.st.com>
Date: Fri, 11 Oct 2024 11:01:32 +0200
From: Amelie Delaunay <amelie.delaunay@...s.st.com>
To: Rob Herring <robh@...nel.org>
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 04/11] dt-bindings: dma: stm32-dma3: prevent linked-list
 refactoring

On 10/10/24 20:14, Rob Herring wrote:
> On Thu, Oct 10, 2024 at 04:27:54PM +0200, Amelie Delaunay wrote:
>> stm32-dma3 driver refactors the linked-list in order to address the memory
>> with the highest possible data width.
>> 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 linked-list refactoring, by setting bit
>> 17 of the 'DMA transfer requirements' bit mask.
>>
>> Signed-off-by: Amelie Delaunay <amelie.delaunay@...s.st.com>
>> ---
>>   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..38c30271f732e0c8da48199a224a88bb647eeca7 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 linked-list refactoring
>> +          0x0: don't prevent driver to refactor the linked-list for optimal performance
>> +          0x1: prevent driver to refactor the linked-list, despite not optimal performance
> 
> Driver settings don't belong in DT. Perhaps reword it in terms of h/w
> constraints (i.e. single transfer limitation).
> 

Thanks for the review and suggestion. I'll reword it in V2. Indeed, it 
is due to single transfer limitation, e.g. for ECC status registers 
transfer.

-bit 17: Prevent additional transfers due to linked-list refactoring
   0x0: don't prevent additional transfers for optimal performance
   0x1: prevent additional transfers to accommodate user constraints 
such as single transfer


Regards,
Amelie

>>   
>>   required:
>>     - compatible
>>
>> -- 
>> 2.25.1
>>