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

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Message-ID: <20241015-dma3-mp25-updates-v2-4-b63e21556ec8@foss.st.com>
Date: Tue, 15 Oct 2024 14:14:40 +0200
From: Amelie Delaunay <amelie.delaunay@...s.st.com>
To: Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...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>
CC: <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>,
        Amelie Delaunay <amelie.delaunay@...s.st.com>
Subject: [PATCH v2 4/9] dt-bindings: dma: stm32-dma3: prevent additional
 transfers

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 these additional transfers, by setting
bit 17 of the 'DMA transfer requirements' bit mask.

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