DMA is preferred for a larger transfers, while PIO is preferred for a smaller transfers to avoid unnecessary DMA overhead. There is no strict size limitations for the PIO-mode transfers, so let's rename the constant for clarity. Tested-by: Thierry Reding <treding@xxxxxxxxxx> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> --- drivers/i2c/busses/i2c-tegra.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c index 0245fc2b5684..e0eb8f5dcd6b 100644 --- a/drivers/i2c/busses/i2c-tegra.c +++ b/drivers/i2c/busses/i2c-tegra.c @@ -131,11 +131,12 @@ #define I2C_PACKET_HEADER_SIZE 12 /* - * Upto I2C_PIO_MODE_MAX_LEN bytes, controller will use PIO mode, - * above this, controller will use DMA to fill FIFO. - * MAX PIO len is 20 bytes excluding packet header. + * I2C Controller will use PIO mode for transfers up to 32 bytes in order to + * avoid DMA overhead, otherwise external APB DMA controller will be used. + * Note that the actual MAX PIO length is 20 bytes because 32 bytes include + * I2C_PACKET_HEADER_SIZE. */ -#define I2C_PIO_MODE_MAX_LEN 32 +#define I2C_PIO_MODE_PREFERRED_LEN 32 /* * msg_end_type: The bus control which need to be send at end of transfer. @@ -1110,7 +1111,7 @@ static int tegra_i2c_xfer_msg(struct tegra_i2c_dev *i2c_dev, xfer_size = msg->len + I2C_PACKET_HEADER_SIZE; xfer_size = ALIGN(xfer_size, BYTES_PER_FIFO_WORD); - i2c_dev->is_curr_dma_xfer = (xfer_size > I2C_PIO_MODE_MAX_LEN) && + i2c_dev->is_curr_dma_xfer = (xfer_size > I2C_PIO_MODE_PREFERRED_LEN) && i2c_dev->dma_buf && !i2c_dev->is_curr_atomic_xfer; tegra_i2c_config_fifo_trig(i2c_dev, xfer_size); -- 2.24.0
