[PATCH v4 5/7] ata: libata: Fix FUA handling in ata_build_rw_tf()

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

If a user issues a write command with the FUA bit set for a device with
NCQ support disabled (that is, the device queue depth was set to 1), the
LBA 48 command WRITE DMA FUA EXT must be used. However,
ata_build_rw_tf() ignores this and first tests if LBA 28 can be used
based on the write command sector and number of blocks. That is, for
small FUA writes at low LBAs, ata_rwcmd_protocol() will cause the write
to fail.

Fix this by preventing the use of LBA 28 for any FUA write request.

Given that the WRITE MULTI FUA EXT command is marked as obsolete iin the
ATA specification since ACS-3 (published in 2013), remove the
ATA_CMD_WRITE_MULTI_FUA_EXT command from the ata_rw_cmds array.

Finally, since the block layer should never issue a FUA read
request, warn in ata_build_rw_tf() if we see such request.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
---
 drivers/ata/libata-core.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 30adae16efff..83bea8591b08 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -552,7 +552,7 @@ static const u8 ata_rw_cmds[] = {
 	0,
 	0,
 	0,
-	ATA_CMD_WRITE_MULTI_FUA_EXT,
+	0,
 	/* pio */
 	ATA_CMD_PIO_READ,
 	ATA_CMD_PIO_WRITE,
@@ -693,6 +693,10 @@ int ata_build_rw_tf(struct ata_queued_cmd *qc, u64 block, u32 n_block,
 	tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
 	tf->flags |= tf_flags;
 
+	/* We should never get a FUA read */
+	WARN_ON_ONCE((tf->flags & ATA_TFLAG_FUA) &&
+		     !(tf->flags & ATA_TFLAG_WRITE));
+
 	if (ata_ncq_enabled(dev)) {
 		/* yay, NCQ */
 		if (!lba_48_ok(block, n_block))
@@ -727,7 +731,8 @@ int ata_build_rw_tf(struct ata_queued_cmd *qc, u64 block, u32 n_block,
 	} else if (dev->flags & ATA_DFLAG_LBA) {
 		tf->flags |= ATA_TFLAG_LBA;
 
-		if (lba_28_ok(block, n_block)) {
+		/* We need LBA48 for FUA writes */
+		if (!(tf->flags & ATA_TFLAG_FUA) && lba_28_ok(block, n_block)) {
 			/* use LBA28 */
 			tf->device |= (block >> 24) & 0xf;
 		} else if (lba_48_ok(block, n_block)) {
@@ -742,9 +747,10 @@ int ata_build_rw_tf(struct ata_queued_cmd *qc, u64 block, u32 n_block,
 			tf->hob_lbah = (block >> 40) & 0xff;
 			tf->hob_lbam = (block >> 32) & 0xff;
 			tf->hob_lbal = (block >> 24) & 0xff;
-		} else
+		} else {
 			/* request too large even for LBA48 */
 			return -ERANGE;
+		}
 
 		if (unlikely(!ata_set_rwcmd_protocol(dev, tf)))
 			return -EINVAL;
-- 
2.38.1