[PATCH v3 0/6] Support ECSPI dynamic burst feature for DMA mode

[Carlos Song]

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.

---
Changes since v2:
* Patch1~4: no change
* Patch5: remove __counted_by from *dma_data, because spi_imx struct
  is allocated with a fixed memory in probe, flexible array is not
  suitable, so just remove it to avoid the build error. Also add
  review-by tag
* Patch6: add review-by tag
Changes since v1:
* Patch1~3:
* Add review-by tag
* Patch4:
  * Add review-by tag
  * Improve patch commit log
* Patch5:
  * Clean up tab instead of space for dma_tx_addr and dma_rx_addr
  * Add  __counted_by(dma_package_num) for dma_data_package *dma_data
  * Move temp and bytes_per_word to if()
  * Add comment for spi_imx_dma_rx_data_handle() and
    spi_imx_dma_tx_data_handle()
  * Use kzalloc instead of kmalloc(x, x | __GFP_ZERO)
  * Use sizeof(*temp) instead of BYTES_PER_32BITS_WORD in suitable place
  * Add comments and fix comments according to discussion
  * Propagate the error value of dma_mapping_error()
  * Use round_down() to replace DIV_ROUND_DOWN_ULL()
  * Improve transfer->error |= SPI_TRANS_FAIL_NO_START judgment for
    better readability
* Patch6:
  * Improve patch commit log
  * Add READ_ONCE for spi_imx->target_aborted
  * Add comments for data length limit
  * Move data length limit to spi_imx_can_dma()

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 | 625 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 519 insertions(+), 106 deletions(-)

-- 
2.34.1