Re: [PATCH 1/6] spi: support simultaneous assertion of multiple CS

[Nuno Sá]

On Tue, Jul 14, 2026 at 02:55:48AM -0300, Jonathan Santos wrote:
> Some SPI controllers allow multiple CS lines to be toggled at the same
> time. The existing code always used CS index 0 when tracking the last
> active CS in spi_set_cs(), and unconditionally set cs_index_mask to
> BIT(0) when parsing DT, both forcing the single CS usage.
> 
> Modify spi_set_cs() to iterate last_cs[] using each logical CS index
> instead of always reading index 0. Modify of_spi_parse_dt() to build
> cs_index_mask from all parsed CS entries rather than hardcoding BIT(0),
> so the controller correctly identifies which CS lines belong to a device
> when asserting them simultaneously.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@xxxxxxxxxx>
> ---

LGTM,

Acked-by: Nuno Sá <nuno.sa@xxxxxxxxxx>

>  drivers/spi/spi.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index d9e6b4b87c89..55fb96fea243 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1090,7 +1090,7 @@ static void spi_set_cs(struct spi_device *spi, bool enable, bool force)
>  	spi->controller->last_cs_index_mask = spi->cs_index_mask;
>  	for (idx = 0; idx < SPI_DEVICE_CS_CNT_MAX; idx++) {
>  		if (enable && idx < spi->num_chipselect)
> -			spi->controller->last_cs[idx] = spi_get_chipselect(spi, 0);
> +			spi->controller->last_cs[idx] = spi_get_chipselect(spi, idx);
>  		else
>  			spi->controller->last_cs[idx] = SPI_INVALID_CS;
>  	}
> @@ -2594,10 +2594,11 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
>  		spi_set_chipselect(spi, idx, cs[idx]);
>  
>  	/*
> -	 * By default spi->chip_select[0] will hold the physical CS number,
> -	 * so set bit 0 in spi->cs_index_mask.
> +	 * Set cs_index_mask to indicate which logical CS indices are active.
> +	 * Each bit corresponds to a logical CS index in the spi->chip_select array.
>  	 */
> -	spi->cs_index_mask = BIT(0);
> +	for (idx = 0; idx < rc; idx++)
> +		spi->cs_index_mask |= BIT(idx);
>  
>  	/* Device speed */
>  	if (!of_property_read_u32(nc, "spi-max-frequency", &value))
> -- 
> 2.34.1
>