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%!


Jisheng Zhang (2):
  spi: dt-bindings: cdns,xspi: add sdma-io-width
  spi: cadence-xspi: support 4bytes sdma-io-width

 .../devicetree/bindings/spi/cdns,xspi.yaml    |  6 +++
 drivers/spi/spi-cadence-xspi.c                | 43 +++++++++++++++++--
 2 files changed, 45 insertions(+), 4 deletions(-)

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2.53.0