[PATCH] SPI: spi bounce buffer has a minimum length

Make sure that spi_write_then_read() can always handle at least 32 bytes
of transfer (total, both directions), minimizing one portability issue.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/spi/spi.c

@@ -522,7 +522,8 @@ int spi_sync(struct spi_device *spi, struct spi_message *message)
 }
 EXPORT_SYMBOL_GPL(spi_sync);
 
-#define	SPI_BUFSIZ	(SMP_CACHE_BYTES)
+/* portable code must never pass more than 32 bytes */
+#define	SPI_BUFSIZ	max(32,SMP_CACHE_BYTES)
 
 static u8	*buf;