[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 <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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;