[PATCH v2] libata: fix ata_id_logical_per_physical_sectors

[Christoph Hellwig <hch@lst.de>]

The value we get from the low byte of the ATA_ID_SECTOR_SIZE word is not not
a plain multiple, but the log of it, so fix the helper to give the correct
answer.  Without this we'll get an incorrect minimal I/O size in the block
limits VPD page for 4k sector drives.

Also change the return value of ata_id_logical_per_physical_sectors to u16
for the unlikely case of very large logical sectors.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/include/linux/ata.h
===================================================================
--- linux-2.6.orig/include/linux/ata.h	2010-01-28 12:24:02.061016474 +0100
+++ linux-2.6/include/linux/ata.h	2010-01-28 13:26:59.270005271 +0100
@@ -647,9 +647,9 @@ static inline int ata_id_has_large_logic
 	return id[ATA_ID_SECTOR_SIZE] & (1 << 13);
 }
 
-static inline u8 ata_id_logical_per_physical_sectors(const u16 *id)
+static inline u16 ata_id_logical_per_physical_sectors(const u16 *id)
 {
-	return id[ATA_ID_SECTOR_SIZE] & 0xf;
+	return 1 << (id[ATA_ID_SECTOR_SIZE] & 0xf);
 }
 
 static inline int ata_id_has_lba48(const u16 *id)