[PATCH 1/2] spi: dt-bindings: cdns,xspi: add sdma-io-width

[Jisheng Zhang <jszhang@kernel.org>]

The cdns xspi controller SDMA data port may support wider I/O width.
Wider I/O width can benefit performance. A simple test with QSPI nor
flash on one arm64 platform:

1 byte io width (default):
 # dd if=/dev/mtdblock0 of=/dev/null bs=8192 count=1000
 1000+0 records in
 1000+0 records out
 8192000 bytes (7.8MB) copied, 1.368735 seconds, 5.7MB/s

4 bytes io width:
 # dd if=/dev/mtdblock0 of=/dev/null bs=8192 count=1000
 1000+0 records in
 1000+0 records out
 8192000 bytes (7.8MB) copied, 1.088787 seconds, 7.2MB/s

Improved by 26.3%!

Add dt binding for sdma-io-width.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 Documentation/devicetree/bindings/spi/cdns,xspi.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/cdns,xspi.yaml b/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
index 38a5795589de..1fd4b6dfd417 100644
--- a/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
+++ b/Documentation/devicetree/bindings/spi/cdns,xspi.yaml
@@ -40,6 +40,12 @@ properties:
   interrupts:
     maxItems: 1
 
+  sdma-io-width:
+    description: Slave DMA data port I/O width (in bytes)
+    $ref: /schemas/types.yaml#/definitions/uint32
+    default: 1
+    enum: [ 1, 4 ]
+
 required:
   - compatible
   - reg
-- 
2.53.0