ECSPI has a low throughput because of no dynamic burst support, it
transfers only one word per frame in DMA mode, causing SCLK stalls
between words due to BURST_LENGTH updates.

This patch set is to support ECSPI dynamic burst feature to help improve
the ECSPI DMA mode performance.

Performance test (spidev_test @10MHz, 4KB):
  Before: tx/rx ~6651.9 kbps
  After:  tx/rx ~9922.2 kbps (~50% improvement)

For compatibility with slow SPI devices, add configurable word delay in
DMA mode. When word delay is set, dynamic burst is disabled and
BURST_LENGTH equals word length.

Also support target DMA mode with enabled dynamic burst.

Carlos Song (6):
  spi: imx: group spi_imx_dma_configure() with spi_imx_dma_transfer()
  spi: imx: introduce helper to clear DMA mode logic
  spi: imx: avoid dmaengine_terminate_all() on TX prep failure
  spi: imx: handle DMA submission errors with dma_submit_error()
  spi: imx: support dynamic burst length for ECSPI DMA mode
  spi: imx: enable DMA mode for target operation

 drivers/spi/spi-imx.c | 620 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 513 insertions(+), 107 deletions(-)

-- 
2.34.1