Re: [PATCH v2 5/9] spi: spi-mem: Allow masters to transfer dummy cycles directly by hardware

[Sowjanya Komatineni <skomatineni@xxxxxxxxxx>]

Sorry mark mixed patches went out.

Will resend v2 and will add other people you have CC'd as well

On 12/11/20 10:33 AM, Mark Brown wrote:
> On Fri, Dec 11, 2020 at 09:01:24AM -0800, Sowjanya Komatineni wrote:
> > This patch adds a flag SPI_MASTER_USES_HW_DUMMY_CYCLES for the controllers
> > that support transfer of dummy cycles by the hardware directly.
> >
> > For controller with this flag set, spi-mem driver will skip dummy bytes
> > transfer in the spi message.
> >
> > Controller drivers can get the number of dummy cycles from spi_message.
> Copying more people who've worked on spi-mem for their review - I've not
> got such a good perspective on controller features.
>
> > Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
> > ---
> >   drivers/spi/spi-mem.c   | 18 +++++++++++-------
> >   include/linux/spi/spi.h |  8 ++++++++
> >   2 files changed, 19 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
> > index f3a3f19..38a523b 100644
> > --- a/drivers/spi/spi-mem.c
> > +++ b/drivers/spi/spi-mem.c
> > @@ -350,13 +350,17 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
> >   	}
> >   
> >   	if (op->dummy.nbytes) {
> > -		memset(tmpbuf + op->addr.nbytes + 1, 0xff, op->dummy.nbytes);
> > -		xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
> > -		xfers[xferpos].len = op->dummy.nbytes;
> > -		xfers[xferpos].tx_nbits = op->dummy.buswidth;
> > -		spi_message_add_tail(&xfers[xferpos], &msg);
> > -		xferpos++;
> > -		totalxferlen += op->dummy.nbytes;
> > +		if (ctlr->flags & SPI_MASTER_USES_HW_DUMMY_CYCLES) {
> > +			msg.dummy_cycles = (op->dummy.nbytes * 8) / op->dummy.buswidth;
> > +		} else {
> > +			memset(tmpbuf + op->addr.nbytes + 1, 0xff, op->dummy.nbytes);
> > +			xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
> > +			xfers[xferpos].len = op->dummy.nbytes;
> > +			xfers[xferpos].tx_nbits = op->dummy.buswidth;
> > +			spi_message_add_tail(&xfers[xferpos], &msg);
> > +			xferpos++;
> > +			totalxferlen += op->dummy.nbytes;
> > +		}
> >   	}
> >   
> >   	if (op->data.nbytes) {
> > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> > index aa09fdc..2024149 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -512,6 +512,8 @@ struct spi_controller {
> >   
> >   #define SPI_MASTER_GPIO_SS		BIT(5)	/* GPIO CS must select slave */
> >   
> > +#define SPI_MASTER_USES_HW_DUMMY_CYCLES	BIT(6)	/* HW dummy bytes transfer */
> > +
> >   	/* flag indicating this is an SPI slave controller */
> >   	bool			slave;
> >   
> > @@ -1022,6 +1024,12 @@ struct spi_message {
> >   	unsigned		actual_length;
> >   	int			status;
> >   
> > +	/*
> > +	 * dummy cycles in the message transfer. This is used by the controller
> > +	 * drivers supports transfer of dummy cycles directly by the hardware.
> > +	 */
> > +	u8			dummy_cycles;
> > +
> >   	/* for optional use by whatever driver currently owns the
> >   	 * spi_message ...  between calls to spi_async and then later
> >   	 * complete(), that's the spi_controller controller driver.
> > --
> > 2.7.4