spi: add ability to validate xfer->bits_per_word in SPI core

Allow SPI masters to define the set of bits_per_word values they support.
If they do this, then the SPI core will reject transfers that attempt to
use an unsupported bits_per_word value. This eliminates the need for each
SPI driver to implement this checking in most cases.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

2 files changed, 16 insertions, 0 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index f996c600eb8c..0cabf1560550 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1377,6 +1377,14 @@ static int __spi_async(struct spi_device *spi, struct spi_message *message)
                         xfer->bits_per_word = spi->bits_per_word;
                 if (!xfer->speed_hz)
                         xfer->speed_hz = spi->max_speed_hz;
+                if (master->bits_per_word_mask) {
+                        /* Only 32 bits fit in the mask */
+                        if (xfer->bits_per_word > 32)
+                                return -EINVAL;
+                        if (!(master->bits_per_word_mask &
+                                        BIT(xfer->bits_per_word - 1)))
+                                return -EINVAL;
+                }
         }
 
         message->spi = spi;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 38c2b925923d..733eb5ee31c5 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -228,6 +228,11 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  *      every chipselect is connected to a slave.
  * @dma_alignment: SPI controller constraint on DMA buffers alignment.
  * @mode_bits: flags understood by this controller driver
+ * @bits_per_word_mask: A mask indicating which values of bits_per_word are
+ *      supported by the driver. Bit n indicates that a bits_per_word n+1 is
+ *      suported. If set, the SPI core will reject any transfer with an
+ *      unsupported bits_per_word. If not set, this value is simply ignored,
+ *      and it's up to the individual driver to perform any validation.
  * @flags: other constraints relevant to this driver
  * @bus_lock_spinlock: spinlock for SPI bus locking
  * @bus_lock_mutex: mutex for SPI bus locking
@@ -301,6 +306,9 @@ struct spi_master {
         /* spi_device.mode flags understood by this controller driver */
         u16                     mode_bits;
 
+        /* bitmask of supported bits_per_word for transfers */
+        u32                     bits_per_word_mask;
+
         /* other constraints relevant to this driver */
         u16                     flags;
 #define SPI_MASTER_HALF_DUPLEX  BIT(0)          /* can't do full duplex */