Hi Wolfram, On Friday 31 October 2014 11:51:15 Wolfram Sang wrote: > Here is my RFC to support DMA with the i2c-sh_mobile core. DMA works nicely > with my tests so far and we save 1 interrupt per transferred byte, yay! Do we have an idea of how much power (or CPU time ?) DMA support could save ? > DMA is opt-in, so if setting it up fails, we will fall back to PIO. The > threshold for selecting DMA is still under test, but probably good enough > already. The major issue currently: This driver uses subsys_initcall() but > at that time DMA is not available, and there is no deferred probe for DMA. > So, switching to module_init() makes DMA work, but this may cause > side-effects for older boards which rely on I2C being available early (to > control some PMIC, for example). This needs some more investigation. Also, > the driver (like all I2C DMA drivers currently) assumes that i2c message > buffers are DMA capable. This is not always true and might need some > assistance from the I2C core. Given the amount of data we could probably use bounce buffers. > Other than that, please test, review, comment. The series is based on > renesas-devel-20141030-v3.18-rc2 with Laurent's series "[PATCH v4 0/5] R-Car > Gen2 DMA Controller driver" on top of it. A git tree can be found here: > > git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git > renesas/i2c-shmobile-dma-experimental > > Thanks, > > Wolfram > > > Wolfram Sang (3): > i2c: sh_mobile: add DMA support > ARM: shmobile: r8a7790: add DMA nodes for IIC > ARM: shmobile: r8a7791: add DMA nodes for IIC > > .../devicetree/bindings/i2c/i2c-sh_mobile.txt | 5 + > arch/arm/boot/dts/r8a7790.dtsi | 8 + > arch/arm/boot/dts/r8a7791.dtsi | 6 + > drivers/i2c/busses/i2c-sh_mobile.c | 203 ++++++++++++++++-- > 4 files changed, 203 insertions(+), 19 deletions(-) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
