1 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 2cc43fa380cb..a0faa18f7b1b 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -245,7 +245,12 @@ struct spi_master {
          */
         u16                     dma_alignment;
 
-        /* setup mode and clock, etc (spi driver may call many times) */
+        /* Setup mode and clock, etc (spi driver may call many times).
+         *
+         * IMPORTANT:  this may be called when transfers to another
+         * device are active.  DO NOT UPDATE SHARED REGISTERS in ways
+         * which could break those transfers.
+         */
         int                     (*setup)(struct spi_device *spi);
 
         /* bidirectional bulk transfers