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

Pratyush Yadav
2020-03-02T09:49:09Z

Hi Boris,

On 27/02/20 05:23PM, Boris Brezillon wrote:
> On Wed, 26 Feb 2020 15:06:54 +0530
> Pratyush Yadav <p.yadav@ti.com> 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@ti.com>
> > ---
> > 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