Even if find out the amount of time MOSI would be required high prior to CS low,
then we would need some sort of MOSI high/low state set with a delay prior to
active CS. That might be enough to support the AD4000 series of devices but,
would it be worth the added complexity?
>
> > +
> > +Peripherals that require this extension must request it by setting the
> > +SPI_MOSI_IDLE_HIGH bit into the mode attribute of their struct spi_device and
>
> Could use inline code formatting for C code bits, e.g. ``struct spi_device``
> ``SPI_MOSI_IDLE_HIGH``, etc.
ok, updated those for v5.
>
> > +call spi_setup(). Controllers that support this extension should indicate it by> +setting SPI_MOSI_IDLE_HIGH in the mode_bits attribute of their struct
> > +spi_controller. The configuration to idle MOSI low is analogous but uses the
> > +SPI_MOSI_IDLE_LOW mode bit.
> > +
> > +
> > THANKS TO
> > ---------
> > Contributors to Linux-SPI discussions include (in alphabetical order,
>
> ...
>
> > index e8e1e798924f..8e50a8559225 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -599,6 +599,12 @@ struct spi_controller {
> > * assert/de-assert more than one chip select at once.
> > */
> > #define SPI_CONTROLLER_MULTI_CS BIT(7)
> > + /*
> > + * The spi-controller is capable of keeping the MOSI line low or high
> > + * when not clocking out data.
> > + */
> > +#define SPI_CONTROLLER_MOSI_IDLE_LOW BIT(8) /* Can idle MOSI low */
> > +#define SPI_CONTROLLER_MOSI_IDLE_HIGH BIT(9) /* Can idle MOSI high */
>
> I don't see where these are used anywhere else in the series. They
> seem redundant with SPI_MOSI_IDLE_LOW and SPI_MOSI_IDLE_HIGH.
>
Good point.
They are currently not being used.
Comparing with what we have for SPI_CONTROLLER_MULTI_CS, I'm thinking it may be
handy to have dt properties to indicate controller MOSI idle capabilities.
Does that sound reasonable?
> >
> > /* Flag indicating if the allocation of this struct is devres-managed */
> > bool devm_allocated;
> > diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
> > index ca56e477d161..ee4ac812b8f8 100644
> > --- a/include/uapi/linux/spi/spi.h
> > +++ b/include/uapi/linux/spi/spi.h
> > @@ -28,7 +28,8 @@
> > #define SPI_RX_OCTAL _BITUL(14) /* receive with 8 wires */
> > #define SPI_3WIRE_HIZ _BITUL(15) /* high impedance turnaround */
> > #define SPI_RX_CPHA_FLIP _BITUL(16) /* flip CPHA on Rx only xfer */
> > -#define SPI_MOSI_IDLE_LOW _BITUL(17) /* leave mosi line low when idle */
> > +#define SPI_MOSI_IDLE_LOW _BITUL(17) /* leave MOSI line low when idle */
> > +#define SPI_MOSI_IDLE_HIGH _BITUL(18) /* leave MOSI line high when idle */
> >
> > /*
> > * All the bits defined above should be covered by SPI_MODE_USER_MASK.
> > @@ -38,6 +39,6 @@
> > * These bits must not overlap. A static assert check should make sure of that.
> > * If adding extra bits, make sure to increase the bit index below as well.
> > */
> > -#define SPI_MODE_USER_MASK (_BITUL(18) - 1)
> > +#define SPI_MODE_USER_MASK (_BITUL(19) - 1)
> >
> > #endif /* _UAPI_SPI_H */
>
