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. All patches have been tested with a Renesas Salvator-X board (r8a7796/M3-W) and a Renesas Lager board (r8a7790/H2). A more detailed test description can be found here: http://elinux.org/Tests:I2C-core-DMA The branch can be found here: git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git renesas/topic/i2c-core-dma-v3 And big kudos to Renesas Electronics for funding this work, thank you very much! Regards, Wolfram Changes since v2: * rebased to v4.13-rc1 * helper functions are not inlined anymore but moved to i2c core * __must_check has been added to the buffer check helper * the release function has been renamed to contain 'dma' as well * documentation updates. Hopefully better wording now * removed the doubled Signed-offs * adding more potentially interested parties to CC 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 | 38 ++++++++++++++++++++ drivers/i2c/busses/i2c-rcar.c | 18 +++++++--- drivers/i2c/busses/i2c-sh_mobile.c | 8 +++-- drivers/i2c/i2c-core-base.c | 68 ++++++++++++++++++++++++++++++++++++ include/linux/i2c.h | 5 +++ 5 files changed, 130 insertions(+), 7 deletions(-) create mode 100644 Documentation/i2c/DMA-considerations -- 2.11.0
