Re: [PATCH 5/6] spi: add rx and tx lane mask to spi_transfer struct

[Nuno Sá]

On Tue, Jul 14, 2026 at 10:18:37AM -0500, David Lechner wrote:
> On 7/14/26 12:56 AM, Jonathan Santos wrote:
> > In SPI_MULTI_LANE_MODE_STRIPE mode, a transfer currently activates all
> > available lanes, but some use cases require operating over a subset of
> > lanes per transfer.
> > 
> > Enable dynamic lane selection for tx and rx by adding new fields to the
> > spi_transfer struct. Controllers that support multi-lane selection must
> > parse the transfer struct to update the rx and tx mask lane-wise.
> > 
> > Peripherals need to set values to the new fields only if multi_lane_mode
> > is set to SPI_MULTI_LANE_MODE_STRIPE and they need to enable at least one
> > lane, not necessary for enabling all lanes.
> 
> As I mentioned in my response to the cover letter, I would hope that we can
> avoid adding this. The idea behind the mutli-lane support when I added it
> was to have a higher-level API so that peripheral drivers don't have to
> figure out which lanes to set when.
> 
> So if the alternate solution I proposed doesn't work, I would like to
> know more about the specific use case before accepting this.

I already acked this one but if we can agree (and from your diagram it
seems we can) on the relation between data lanes and CS lines, I think
what you proposed makes more sense and keeps things much easier and high
level for peripherals. But just my 2 cents, Jonathan has the system
knowledge and usecases so he can better reason about this.

- Nuno Sá

> 
> > 
> > Signed-off-by: Jonathan Santos <Jonathan.Santos@xxxxxxxxxx>
> > ---
> >  include/linux/spi/spi.h | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> > index a9988db3fe2f..f4473d53b6b5 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -986,6 +986,12 @@ struct spi_res {
> >   *      (SPI_NBITS_SINGLE) is used.
> >   * @multi_lane_mode: How to serialize data on multiple lanes. One of the
> >   *      SPI_MULTI_LANE_MODE_* values.
> > + * @rx_lane_mask: Bitmask of lanes to use for receive in
> > + *      SPI_MULTI_LANE_MODE_STRIPE mode. Each set bit enables the corresponding
> > + *      lane. If 0 all available lanes are used.
> > + * @tx_lane_mask: Bitmask of lanes to use for transmit in
> > + *      SPI_MULTI_LANE_MODE_STRIPE mode. Each set bit enables the corresponding
> > + *      lane. If 0 all available lanes are used.
> >   * @len: size of rx and tx buffers (in bytes)
> >   * @speed_hz: Select a speed other than the device default for this
> >   *      transfer. If 0 the default (from @spi_device) is used.
> > @@ -1131,6 +1137,8 @@ struct spi_transfer {
> >  #define SPI_MULTI_LANE_MODE_STRIPE	1 /* one data word per lane */
> >  #define SPI_MULTI_LANE_MODE_MIRROR	2 /* same word sent on all lanes */
> >  	unsigned	multi_lane_mode: 2;
> > +	unsigned	rx_lane_mask: 8;
> > +	unsigned	tx_lane_mask: 8;
> 
> Just make it u8 instead of using bitfield.
> 
> >  
> >  	unsigned	timestamped:1;
> >  	bool		dtr_mode;
>