Re: [PATCH V3 3/3] i2c: tegra: Add DMA Support

Dmitry Osipenko
2019-01-26T21:24:43Z

26.01.2019 6:57, Sowjanya Komatineni пишет:
> 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 adding overhead on CPU for large transfers.
>
> DMA mode is helpful for Large transfers during downloading or
> uploading FW over I2C to some external devices.
>
> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
>
> ---

Seems there are good news, APB DMA could access IRAM. Quote from TRM: "The source may be DRAM or IRAM, and the destination location could be devices placed on APB Bus; or vice versa". Hence it shall be much more efficient to use IRAM for the DMA buffer, please consider that variant.