So, after revisiting old mail threads and taking part in a similar discussion on the USB list, here is what I cooked up to document and ease DMA handling for I2C within Linux. Please have a look at the documentation introduced in patch 2 for further details.
The branch can be found here: git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/topic/i2c-core-dma And big kudos to Renesas Electronics for funding this work, thank you very much! Regards, Wolfram Changes since RFC: * the helper i2c_check_msg_for_dma() can optionally take a pointer and then it will attach a bounce buffer to it in case the message buffer is not DMA safe * a second helper was added. i2c_release_bounce_buf() will copy data back to the message buffer and release the bounce buffer * the documentation has been extended to match the above * no ifdeffery around CONFIG_DMA_API_DEBUG anymore. The I2C core behaviour should not depend on such symbols. * the i2c-sh_mobile driver has been updated to use bounce buffers Wolfram Sang (4): i2c: add helpers to ease DMA handling i2c: add docs to clarify DMA handling i2c: sh_mobile: use helper to decide if DMA is useful i2c: rcar: check for DMA-capable buffers Documentation/i2c/DMA-considerations | 37 ++++++++++++++++++++ drivers/i2c/busses/i2c-rcar.c | 18 +++++++--- drivers/i2c/busses/i2c-sh_mobile.c | 8 +++-- include/linux/i2c.h | 65 ++++++++++++++++++++++++++++++++++++ 4 files changed, 121 insertions(+), 7 deletions(-) create mode 100644 Documentation/i2c/DMA-considerations -- 2.11.0
