[PATCH] SPI: devices can require LSB-first encodings

Add spi_device hook for LSB-first word encoding, and update all the
(in-tree) controller drivers to reject such devices.  Eventually,
some controller drivers will be updated to support lsb-first encodings
on the wire; no current drivers need this.

Signed-off-by: David Brownell <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/spi/spi_bitbang.c b/drivers/spi/spi_bitbang.c
index 6c3da64d609a..0f7f5c64391c 100644
--- a/drivers/spi/spi_bitbang.c
+++ b/drivers/spi/spi_bitbang.c
@@ -187,13 +187,22 @@ int spi_bitbang_setup(struct spi_device *spi)
 	if (!spi->max_speed_hz)
 		return -EINVAL;
 
+	bitbang = spi_master_get_devdata(spi->master);
+
+	/* REVISIT: some systems will want to support devices using lsb-first
+	 * bit encodings on the wire.  In pure software that would be trivial,
+	 * just bitbang_txrx_le_cphaX() routines shifting the other way, and
+	 * some hardware controllers also have this support.
+	 */
+	if ((spi->mode & SPI_LSB_FIRST) != 0)
+		return -EINVAL;
+
 	if (!cs) {
 		cs = kzalloc(sizeof *cs, SLAB_KERNEL);
 		if (!cs)
 			return -ENOMEM;
 		spi->controller_state = cs;
 	}
-	bitbang = spi_master_get_devdata(spi->master);
 
 	if (!spi->bits_per_word)
 		spi->bits_per_word = 8;