libata: Clarify ata_set_lba_range_entries function

ata_set_lba_range_entries used the variable max for two different things
which was confusing.  Make the function take a buffer size in bytes as
argument and return the used buffer size upon completion.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-scsi.c

@@ -2972,7 +2972,7 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 		goto invalid_fld;
 
 	buf = page_address(sg_page(scsi_sglist(scmd)));
-	size = ata_set_lba_range_entries(buf, 512 / 8, block, n_block);
+	size = ata_set_lba_range_entries(buf, 512, block, n_block);
 
 	tf->protocol = ATA_PROT_DMA;
 	tf->hob_feature = 0;

include/linux/ata.h

@@ -982,17 +982,17 @@ static inline void ata_id_to_hd_driveid(u16 *id)
 }
 
 /*
- * Write up to 'max' LBA Range Entries to the buffer that will cover the
- * extent from sector to sector + count.  This is used for TRIM and for
- * ADD LBA(S) TO NV CACHE PINNED SET.
+ * Write LBA Range Entries to the buffer that will cover the extent from
+ * sector to sector + count.  This is used for TRIM and for ADD LBA(S)
+ * TO NV CACHE PINNED SET.
  */
-static inline unsigned ata_set_lba_range_entries(void *_buffer, unsigned max,
-						u64 sector, unsigned long count)
+static inline unsigned ata_set_lba_range_entries(void *_buffer,
+		unsigned buf_size, u64 sector, unsigned long count)
 {
 	__le64 *buffer = _buffer;
-	unsigned i = 0;
+	unsigned i = 0, used_bytes;
 
-	while (i < max) {
+	while (i < buf_size / 8 ) { /* 6-byte LBA + 2-byte range per entry */
 		u64 entry = sector |
 			((u64)(count > 0xffff ? 0xffff : count) << 48);
 		buffer[i++] = __cpu_to_le64(entry);
@@ -1002,9 +1002,9 @@ static inline unsigned ata_set_lba_range_entries(void *_buffer, unsigned max,
 		sector += 0xffff;
 	}
 
-	max = ALIGN(i * 8, 512);
-	memset(buffer + i, 0, max - i * 8);
-	return max;
+	used_bytes = ALIGN(i * 8, 512);
+	memset(buffer + i, 0, used_bytes - i * 8);
+	return used_bytes;
 }
 
 static inline int is_multi_taskfile(struct ata_taskfile *tf)