1 files changed, 16 insertions, 9 deletions

diff --git a/include/linux/spi/mcp23s08.h b/include/linux/spi/mcp23s08.h
index 835ddf47d45c..22ef107d7704 100644
--- a/include/linux/spi/mcp23s08.h
+++ b/include/linux/spi/mcp23s08.h
@@ -1,18 +1,25 @@
 
-/* FIXME driver should be able to handle all four slaves that
- * can be hooked up to each chipselect, as well as IRQs...
- */
+/* FIXME driver should be able to handle IRQs...  */
+
+struct mcp23s08_chip_info {
+        bool    is_present;             /* true iff populated */
+        u8      pullups;                /* BIT(x) means enable pullup x */
+};
 
 struct mcp23s08_platform_data {
-        /* four slaves can share one SPI chipselect */
-        u8              slave;
+        /* Four slaves (numbered 0..3) can share one SPI chipselect, and
+         * will provide 8..32 GPIOs using 1..4 gpio_chip instances.
+         */
+        struct mcp23s08_chip_info       chip[4];
 
-        /* number assigned to the first GPIO */
+        /* "base" is the number of the first GPIO.  Dynamic assignment is
+         * not currently supported, and even if there are gaps in chip
+         * addressing the GPIO numbers are sequential .. so for example
+         * if only slaves 0 and 3 are present, their GPIOs range from
+         * base to base+15.
+         */
         unsigned        base;
 
-        /* pins with pullups */
-        u8              pullups;
-
         void            *context;       /* param to setup/teardown */
 
         int             (*setup)(struct spi_device *spi,