[PATCH v5 2/2] libata-scsi: avoid repeated calculation of number of TRIM ranges

[tom.ty89@gmail.com]

From: Tom Yan <tom.ty89@gmail.com>

Currently libata statically allows only 1-block (512-byte) payload
for each TRIM command. Each payload can carry 64 TRIM ranges since
each range requires 8 bytes.

It is silly to keep doing the calculation (512 / 8) in different
places. Hence, define the new ATA_MAX_TRIM_RNUM for the result.

Signed-off-by: Tom Yan <tom.ty89@gmail.com>

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index a1f061a..82739be 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2314,7 +2314,7 @@ static unsigned int ata_scsiop_inq_b0(struct ata_scsi_args *args, u8 *rbuf)
 	 * with the unmap bit set.
 	 */
 	if (ata_id_has_trim(args->id)) {
-		put_unaligned_be64(65535 * 512 / 8, &rbuf[36]);
+		put_unaligned_be64(65535 * ATA_MAX_TRIM_RNUM, &rbuf[36]);
 		put_unaligned_be32(1, &rbuf[28]);
 	}
 
@@ -3306,8 +3306,8 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
 
 	buf = page_address(sg_page(scsi_sglist(scmd)));
 
-	if (n_block <= 65535 * 512 / 8)
-		size = ata_set_lba_range_entries(buf, 512, block, n_block);
+	if (n_block <= 65535 * ATA_MAX_TRIM_RNUM)
+		size = ata_set_lba_range_entries(buf, ATA_MAX_TRIM_RNUM, block, n_block);
 	else
 		goto invalid_fld;
 
diff --git a/include/linux/ata.h b/include/linux/ata.h
index 99346be..ce59500 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -48,6 +48,7 @@ enum {
 	ATA_MAX_SECTORS_1024    = 1024,
 	ATA_MAX_SECTORS_LBA48	= 65535,/* TODO: 65536? */
 	ATA_MAX_SECTORS_TAPE	= 65535,
+	ATA_MAX_TRIM_RNUM	= 64,	/* 512-byte payload / (6-byte LBA + 2-byte range per entry) */
 
 	ATA_ID_WORDS		= 256,
 	ATA_ID_CONFIG		= 0,
@@ -1071,7 +1072,7 @@ static inline unsigned ata_set_lba_range_entries(void *_buffer,
 	__le64 *buffer = _buffer;
 	unsigned i = 0, used_bytes;
 
-	while (i < buf_size / 8 ) { /* 6-byte LBA + 2-byte range per entry */
+	while (i < buf_size) {
 		u64 entry = sector |
 			((u64)(count > 0xffff ? 0xffff : count) << 48);
 		buffer[i++] = __cpu_to_le64(entry);
-- 
2.9.0