Re: [PATCH v4 6/9] spi: introduce SPI ancillary device with lanes

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 20 Oct 2026 22:58:01 -0300
Jonathan Santos <Jonathan.Santos@analog.com> wrote:

> The existing spi_new_ancillary_device() creates an ancillary SPI device
> but does not consider the parent's lane map. In multi-device setups where
> each sub-device's chip-select is bound to a dedicated data lane, there is
> no way to bind an ancillary device to an arbitrary lane index.
> 
> Introduce spi_new_ancillary_device_with_lane() and
> devm_spi_new_ancillary_device_with_lane(), which accept rx_lane_idx and
> tx_lane_idx parameters to select a specific lane from the parent's
> rx_lane_map and tx_lane_map respectively. The resulting ancillary device
> is registered with a single RX and TX lane, keeping it independent from
> the other sub-devices sharing the same controller.

The multiple-data-lanes.rst doc doesn't me make it clear if for the 
lanes are all one wide, or if it is fine to have 2 lanes each
of width 4.  Either way I'd expect more parameters to be needed.
The AD7786 has diagrams of two devices, bus width 2 for each.

> 
> While at it, fix the spi_new_ancillary_device() documentation, which
> claimed it returns 0 on success instead of a pointer.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
> ---
> Changes in v4:
> * Don't use extern for the new declarations of the ancillary functions from
>   spi.h.
> 
> Changes in v3:
> * Refactored code using helper function to reduce duplicated code.
> 
> Changes in v2:
> * New patch.
> ---
>  drivers/spi/spi.c       | 116 +++++++++++++++++++++++++++++++++++-----
>  include/linux/spi/spi.h |   8 +++
>  2 files changed, 110 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 53d6ab4ce8a3..30103bffad33 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -2918,20 +2918,12 @@ static void of_register_spi_devices(struct spi_controller *ctlr)
>  static void of_register_spi_devices(struct spi_controller *ctlr) { }
>  #endif
>  
> -/**
> - * spi_new_ancillary_device() - Register ancillary SPI device
> - * @spi:         Pointer to the main SPI device registering the ancillary device
> - * @chip_select: Chip Select of the ancillary device
> - *
> - * Register an ancillary SPI device; for example some chips have a chip-select
> - * for normal device usage and another one for setup/firmware upload.
> - *
> - * This may only be called from main SPI device's probe routine.
> - *
> - * Return: 0 on success; negative errno on failure
> - */
> -struct spi_device *spi_new_ancillary_device(struct spi_device *spi,
> -					     u8 chip_select)
> +#define SPI_UNDEFINED_LANE	-1
> +
> +static struct spi_device *__spi_new_ancillary_device(struct spi_device *spi,
> +						     u8 chip_select,
> +						     int rx_lane_idx,
> +						     int tx_lane_idx)
>  {
>  	struct spi_controller *ctlr = spi->controller;
>  	struct spi_device *ancillary;
> @@ -2958,6 +2950,21 @@ struct spi_device *spi_new_ancillary_device(struct spi_device *spi,
>  	 */
>  	ancillary->cs_index_mask = BIT(0);
>  
> +	if (rx_lane_idx >= spi->num_rx_lanes || tx_lane_idx >= spi->num_tx_lanes) {
> +		rc = -EINVAL;
> +		goto err_out;
> +	}
> +
> +	if (rx_lane_idx != SPI_UNDEFINED_LANE) {
> +		ancillary->rx_lane_map[0] = spi->rx_lane_map[rx_lane_idx];
> +		ancillary->num_rx_lanes = 1;
> +	}
> +
> +	if (tx_lane_idx != SPI_UNDEFINED_LANE) {
> +		ancillary->tx_lane_map[0] = spi->tx_lane_map[tx_lane_idx];
> +		ancillary->num_tx_lanes = 1;
> +	}
> +
>  	WARN_ON(!mutex_is_locked(&ctlr->add_lock));
>  
>  	/* Register the new device, passing the parent to skip CS conflict check */