linux-kernel - [PATCH v6 0/7] spi: spi-fsl-dspi: Target mode improvements

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Message-Id: <20250902-james-nxp-spi-dma-v6-0-f7aa2c5e56e2@linaro.org>
Date: Tue, 02 Sep 2025 13:44:52 +0100
From: James Clark <james.clark@...aro.org>
To: Vladimir Oltean <olteanv@...il.com>, Mark Brown <broonie@...nel.org>, 
 Vladimir Oltean <vladimir.oltean@....com>, Arnd Bergmann <arnd@...db.de>, 
 Larisa Grigore <larisa.grigore@....com>, Frank Li <Frank.li@....com>, 
 Christoph Hellwig <hch@....de>
Cc: linux-spi@...r.kernel.org, imx@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, James Clark <james.clark@...aro.org>, 
 Frank Li <Frank.Li@....com>
Subject: [PATCH v6 0/7] spi: spi-fsl-dspi: Target mode improvements

Improve usability of target mode by reporting FIFO errors and increasing
the buffer size when DMA is used. While we're touching DMA stuff also
switch to non-coherent memory, although this is unrelated to target
mode.

With the combination of the commit to increase the DMA buffer size and
the commit to use non-coherent memory, the host mode performance figures
are as follows on S32G3:

  # spidev_test --device /dev/spidev1.0 --bpw 8 --size <test_size> --cpha --iter 10000000 --speed 10000000

  Coherent (4096 byte transfers): 6534 kbps
  Non-coherent:                   7347 kbps

  Coherent (16 byte transfers):    447 kbps
  Non-coherent:                    448 kbps

Just for comparison running the same test in XSPI mode:

  4096 byte transfers:            2143 kbps
  16 byte transfers:               637 kbps

These tests required hacking S32G3 to use DMA in host mode, although
the figures should be representative of target mode too where DMA is
used. And the other devices that use DMA in host mode should see similar
improvements.

Signed-off-by: James Clark <james.clark@...aro.org>
---
Changes in v6:
- Indentation fix
- Fix trailers in first commit
- Explain reasoning for "spi: spi-fsl-dspi: Stub out DMA functions"
- Link to v5: https://lore.kernel.org/r/20250829-james-nxp-spi-dma-v5-0-3246957a6ea9@linaro.org

Changes in v5:
- Change some ints to size_t for consistency
- Separate change for making buffer size a page and making target mode
  buffer larger
- Explain reasoning for target mode buffer size change in commit message
- Replace an if with a min()
- Drop applied fixes: commit
- Take Vladimir's change to separate -EINPROGRESS and cur_msg->status
  changes and fix the bug
- Get max segment size from dmaengine rather than hardcoding it and
  store the size in struct fsl_dspi_dma
- Link to v4: https://lore.kernel.org/r/20250627-james-nxp-spi-dma-v4-0-178dba20c120@linaro.org

Changes in v4:
- Fix !CONFIG_DMA_ENGINE build (and actually test it this time)
- Reword completion counter comment
- Reword some commit messages
- Reset tries in dspi_poll() for each transfer
- Check for fifo errors in dspi_poll() before checking for completion
- Link to v3: https://lore.kernel.org/r/20250624-james-nxp-spi-dma-v3-0-e7d574f5f62c@linaro.org

Changes in v3:
- Stub out DMA functions in the driver so no-DMA builds work
- Link to v2: https://lore.kernel.org/r/20250613-james-nxp-spi-dma-v2-0-017eecf24aab@linaro.org

Changes in v2:
- Store status in cur_msg->status rather than adding xfer_status
- Show exact underflow/overflow flags in error message
- Rate limit error messages
- Add a comment about resetting the completion counter prior to transfer
- Rename dspi_is_fifo_overflow() -> dspi_fifo_error()
- Add performance figures to cover letter
- Rebase onto https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git/for-next
  to avoid some conflicts
- Link to v1: https://lore.kernel.org/r/20250609-james-nxp-spi-dma-v1-0-2b831e714be2@linaro.org

---
James Clark (7):
      spi: fsl-dspi: Avoid using -EINPROGRESS error code
      spi: fsl-dspi: Store status directly in cur_msg->status
      spi: spi-fsl-dspi: Stub out DMA functions
      spi: spi-fsl-dspi: Use non-coherent memory for DMA
      spi: spi-fsl-dspi: Use whole page for DMA buffers
      spi: spi-fsl-dspi: Increase target mode DMA buffer size
      spi: spi-fsl-dspi: Report FIFO overflows as errors

 drivers/spi/spi-fsl-dspi.c | 232 +++++++++++++++++++++++++++++++--------------
 1 file changed, 162 insertions(+), 70 deletions(-)
---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250522-james-nxp-spi-dma-a997ebebfb6b

Best regards,
-- 
James Clark <james.clark@...aro.org>