1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/spi/spi_bitbang.h b/include/linux/spi/spi_bitbang.h
index 8dfe61a445f4..c961fe9bf3eb 100644
--- a/include/linux/spi/spi_bitbang.h
+++ b/include/linux/spi/spi_bitbang.h
@@ -31,8 +31,15 @@ struct spi_bitbang {
         struct spi_master       *master;
 
         void    (*chipselect)(struct spi_device *spi, int is_on);
+#define BITBANG_CS_ACTIVE       1       /* normally nCS, active low */
+#define BITBANG_CS_INACTIVE     0
 
+        /* txrx_bufs() may handle dma mapping for transfers that don't
+         * already have one (transfer.{tx,rx}_dma is zero), or use PIO
+         */
         int     (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
+
+        /* txrx_word[SPI_MODE_*]() just looks like a shift register */
         u32     (*txrx_word[4])(struct spi_device *spi,
                         unsigned nsecs,
                         u32 word, u8 bits);