[PATCH] SPI: busnum == 0 needs to work

We need to be able to have a "SPI bus 0" matching chip numbering; but
that number was wrongly used to flag dynamic allocation of a bus number.

This patch resolves that issue; now negative numbers trigger dynamic alloc.

It also updates the how-to-write-a-controller-driver overview to mention
this stuff.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 77add901691d..e928c0dcc297 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -172,13 +172,13 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
 struct spi_master {
         struct class_device     cdev;
 
-        /* other than zero (== assign one dynamically), bus_num is fully
+        /* other than negative (== assign one dynamically), bus_num is fully
          * board-specific.  usually that simplifies to being SOC-specific.
-         * example:  one SOC has three SPI controllers, numbered 1..3,
+         * example:  one SOC has three SPI controllers, numbered 0..2,
          * and one board's schematics might show it using SPI-2.  software
          * would normally use bus_num=2 for that controller.
          */
-        u16                     bus_num;
+        s16                     bus_num;
 
         /* chipselects will be integral to many controllers; some others
          * might use board-specific GPIOs.