[PATCH 7/9] hpsa: Clarify calculation of padding for commandlist structure

Stephen M. Cameron
2010-02-25T20:00:13Z

hpsa: Clarify calculation of padding for commandlist structure

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
---
drivers/scsi/hpsa_cmd.h | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/hpsa_cmd.h b/drivers/scsi/hpsa_cmd.h
index 3e0abdf..43b6f1c 100644
--- a/drivers/scsi/hpsa_cmd.h
+++ b/drivers/scsi/hpsa_cmd.h
@@ -313,12 +313,18 @@ struct CommandList {
void *scsi_cmd;

/* on 64 bit architectures, to get this to be 32-byte-aligned
- * it so happens we need no padding, on 32 bit systems,
- * we need 8 bytes of padding. This does that.
+ * it so happens we need PAD_64 bytes of padding, on 32 bit systems,
+ * we need PAD_32 bytes of padding (see below). This does that.
+ * If it happens that 64 bit and 32 bit systems need different
+ * padding, PAD_32 and PAD_64 can be set independently, and.
+ * the code below will do the right thing.
*/
-#define COMMANDLIST_PAD ((8 - sizeof(long))/4 * 8)
+#define IS_32_BIT ((8 - sizeof(long))/4)
+#define IS_64_BIT (!IS_32_BIT)
+#define PAD_32 (8)
+#define PAD_64 (0)
+#define COMMANDLIST_PAD (IS_32_BIT * PAD_32 + IS_64_BIT * PAD_64)
u8 pad[COMMANDLIST_PAD];
-
};

/* Configuration Table Structure */