Re: [PATCH v2 02/11] spi: set mode bits for "spi-rx-dtr" and "spi-tx-dtr"

[Pratyush Yadav]

Hi Boris,

On 27/02/20 05:23PM, Boris Brezillon wrote:
> On Wed, 26 Feb 2020 15:06:54 +0530
> Pratyush Yadav <p.yadav@xxxxxx> wrote:
> 
> > These two DT properties express DTR receive and transmit capabilities of
> > a SPI flash and controller. Introduce two new mode bits: SPI_RX_DTR and
> > SPI_TX_DTR which correspond to the new DT properties. Set these bits
> > when the two corresponding properties are present in the device tree.
> > Also update the detection of unsupported mode bits to include the new
> > bits.
> > 
> > Signed-off-by: Pratyush Yadav <p.yadav@xxxxxx>
> > ---
> >  drivers/spi/spi.c       | 10 +++++++++-
> >  include/linux/spi/spi.h |  2 ++
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> > index 38b4c78df506..25c8ed9343f9 100644
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -1927,6 +1927,13 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
> >  		}
> >  	}
> >  
> > +	/* Device DTR mode. */
> > +	if (of_property_read_bool(nc, "spi-tx-dtr"))
> > +		spi->mode |= SPI_TX_DTR;
> > +
> > +	if (of_property_read_bool(nc, "spi-rx-dtr"))
> > +		spi->mode |= SPI_RX_DTR;
> > +
> 
> If this DTR mode is only used in spi-mem, maybe we shouldn't add those
> flags. SPI mem devices are usually smart enough to advertise what they
> support, and the subsystem in charge of those devices (in this specific
> case, spi-nor) will check what the controller supports
> using spi_mem_supports_op(). The only case we might have to deal with
> at some point is board level limitations (disabling DTR because the
> routing prevents using this mode).
 
Yes, being able to handle board-level limitations is the main reason 
behind this change. There should be a way to over-ride the use of DTR 
for a given board. And IIUC, SPI allows doing the same for Rx and Tx 
buswidth. So I don't see why we should deviate from that model.

> >  	if (spi_controller_is_slave(ctlr)) {
> >  		if (!of_node_name_eq(nc, "slave")) {
> >  			dev_err(&ctlr->dev, "%pOF is not called 'slave'\n",
> > @@ -3252,7 +3259,8 @@ int spi_setup(struct spi_device *spi)
> >  		bad_bits &= ~SPI_CS_HIGH;
> >  	ugly_bits = bad_bits &
> >  		    (SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL |
> > -		     SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL);
> > +		     SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL |
> > +		     SPI_TX_DTR  | SPI_RX_DTR);
> >  	if (ugly_bits) {
> >  		dev_warn(&spi->dev,
> >  			 "setup: ignoring unsupported mode bits %x\n",
> > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> > index 6d16ba01ff5a..bf1108318389 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -183,6 +183,8 @@ struct spi_device {
> >  #define	SPI_TX_OCTAL	0x2000			/* transmit with 8 wires */
> >  #define	SPI_RX_OCTAL	0x4000			/* receive with 8 wires */
> >  #define	SPI_3WIRE_HIZ	0x8000			/* high impedance turnaround */
> > +#define SPI_RX_DTR	0x10000			/* receive in DTR mode */
> > +#define SPI_TX_DTR	0x20000			/* transmit in DTR mode */
> >  	int			irq;
> >  	void			*controller_state;
> >  	void			*controller_data;
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments India