spi: add software implementation for SPI_CS_WORD

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@lechnology.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index ec395a6baf9cacbae1830cf062fb40ae7e778f62..be73d236919f067a9ad5be3123024ff1f417a22f 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2774,8 +2774,10 @@ 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) {
@@ -2829,6 +2831,33 @@ 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