On Wed, 12 Sep 2018 19:39:18 -0500
David Lechner <david@xxxxxxxxxxxxxx> wrote:
> This adds a default software implementation for the SPI_CS_WORD flag for
> controllers that don't have such a feature.
>
> The SPI_CS_WORD flag indicates that the CS line should be toggled
> between each word sent, not just between each transfer. The
> implementation works by using existing functions to split transfers into
> one-word-sized transfers and sets the cs_change bit for each of the
> new transfers.
>
> Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
Looks good to me but I'm not that familiar with this code..
Acked-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> drivers/spi/spi.c | 31 +++++++++++++++++++++++++++++++-
> 1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 9da0bc5a036c..84518ed58872 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -2783,8 +2783,10 @@ int spi_setup(struct spi_device *spi)
> return -EINVAL;
> /* help drivers fail *cleanly* when they need options
> * that aren't supported with their current controller
> + * SPI_CS_WORD has a fallback software implementation,
> + * so it is ignored here.
> */
> - bad_bits = spi->mode & ~spi->controller->mode_bits;
> + bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD);
> ugly_bits = bad_bits &
> (SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD);
> if (ugly_bits) {
> @@ -2838,6 +2840,33 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
> if (list_empty(&message->transfers))
> return -EINVAL;
>
> + /* If an SPI controller does not support toggling the CS line on each
> + * transfer (indicated by the SPI_CS_WORD flag), we can emulate it by
> + * splitting transfers into one-word transfers and ensuring that
> + * cs_change is set for each transfer.
> + */
> + if ((spi->mode & SPI_CS_WORD) && !(ctlr->mode_bits & SPI_CS_WORD)) {
> + size_t maxsize;
> + int ret;
> +
> + maxsize = (spi->bits_per_word + 7) / 8;
> +
> + /* spi_split_transfers_maxsize() requires message->spi */
> + message->spi = spi;
> +
> + ret = spi_split_transfers_maxsize(ctlr, message, maxsize,
> + GFP_KERNEL);
> + if (ret)
> + return ret;
> +
> + list_for_each_entry(xfer, &message->transfers, transfer_list) {
> + /* don't change cs_change on the last entry in the list */
> + if (list_is_last(&xfer->transfer_list, &message->transfers))
> + break;
> + xfer->cs_change = 1;
> + }
> + }
> +
> /* Half-duplex links include original MicroWire, and ones with
> * only one data pin like SPI_3WIRE (switches direction) or where
> * either MOSI or MISO is missing. They can also be caused by
