On Tue, Feb 12, 2019 at 11:06:46AM -0800, Sowjanya Komatineni wrote: > This patch adds DMA support for Tegra I2C. > > Tegra I2C TX and RX FIFO depth is 8 words. PIO mode is used for > transfer size of the max FIFO depth and DMA mode is used for > transfer size higher than max FIFO depth to save CPU overhead. > > PIO mode needs full intervention of CPU to fill or empty FIFO's > and also need to service multiple data requests interrupt for the > same transaction. This adds delay between data bytes of the same > transfer when CPU is fully loaded and some slave devices has > internal timeout for no bus activity and stops transaction to > avoid bus hang. DMA mode is helpful in such cases. > > DMA mode is also helpful for Large transfers during downloading or > uploading FW over I2C to some external devices. > > Tegra210 and prior Tegra chips use APBDMA driver which is replaced > with GPCDMA on Tegra186 and Tegra194. > This patch uses has_apb_dma flag in hw_feature to differentiate > DMA driver change between Tegra chipset. > > APBDMA driver is registered from module-init level and this patch > also has a change to register I2C driver at module-init level > rather than subsys-init to avoid deferring I2C probe till APBDMA > driver is registered. > > Acked-by: Thierry Reding <treding@xxxxxxxxxx> > Reviewed-by: Dmitry Osipenko <digetx@xxxxxxxxx> > Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx> > Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx> Not directly related to your code, but maybe someone is interested in fixing this rightful checkpatch comment somewhen later: WARNING: Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON() #332: FILE: drivers/i2c/busses/i2c-tegra.c:791: + BUG();
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