[no subject]

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 */
>