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 <[email protected]> > --- > 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
