Hi Sowjanya,
On 17/12/20 12:28PM, Sowjanya Komatineni wrote:
> This patch marks dummy transfer by setting dummy_data bit to 1.
>
> Controllers supporting dummy transfer by hardware use this bit field
> to skip software transfer of dummy bytes and use hardware dummy bytes
> transfer.
What is the benefit you get from this change? You add complexity in
spi-mem and the controller driver, so that must come with some benefits.
Here I don't see any. The transfer will certainly take the same amount
of time because the number or period of the dummy cycles has not
changed. So why is this needed?
> Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
> ---
> drivers/spi/spi-mem.c | 1 +
> include/linux/spi/spi.h | 2 ++
> 2 files changed, 3 insertions(+)
>
> diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
> index f3a3f19..c64371c 100644
> --- a/drivers/spi/spi-mem.c
> +++ b/drivers/spi/spi-mem.c
> @@ -354,6 +354,7 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
> xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
> xfers[xferpos].len = op->dummy.nbytes;
> xfers[xferpos].tx_nbits = op->dummy.buswidth;
> + xfers[xferpos].dummy_data = 1;
> spi_message_add_tail(&xfers[xferpos], &msg);
> xferpos++;
> totalxferlen += op->dummy.nbytes;
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index aa09fdc..708f2f5 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -827,6 +827,7 @@ extern void spi_res_release(struct spi_controller *ctlr,
> * transfer. If 0 the default (from @spi_device) is used.
> * @bits_per_word: select a bits_per_word other than the device default
> * for this transfer. If 0 the default (from @spi_device) is used.
> + * @dummy_data: indicates transfer is dummy bytes transfer.
> * @cs_change: affects chipselect after this transfer completes
> * @cs_change_delay: delay between cs deassert and assert when
> * @cs_change is set and @spi_transfer is not the last in @spi_message
> @@ -939,6 +940,7 @@ struct spi_transfer {
> struct sg_table tx_sg;
> struct sg_table rx_sg;
>
> + unsigned dummy_data:1;
> unsigned cs_change:1;
> unsigned tx_nbits:3;
> unsigned rx_nbits:3;
> --
> 2.7.4
>
--
Regards,
Pratyush Yadav
Texas Instruments India
