[PATCH v3 4/6] 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 test if LBA 28 can be used.
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.
While at it, also early test if the request is a FUA read and fail these
requests for the NCQ-disabled case instead of relying on
ata_rwcmd_protocol() returning an error.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
---
 drivers/ata/libata-core.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 81b20ffb1554..fea06f41f371 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -725,9 +725,21 @@ int ata_build_rw_tf(struct ata_queued_cmd *qc, u64 block, u32 n_block,
 		    class == IOPRIO_CLASS_RT)
 			tf->hob_nsect |= ATA_PRIO_HIGH << ATA_SHIFT_PRIO;
 	} else if (dev->flags & ATA_DFLAG_LBA) {
+		bool lba28_ok;
+
+		if (tf->flags & ATA_TFLAG_FUA) {
+			/* FUA reads are not defined */
+			if (!(tf->flags & ATA_TFLAG_WRITE))
+				return -EINVAL;
+			/* We need LBA48 / WRITE DMA FUA EXT for FUA writes */
+			lba28_ok = false;
+		} else {
+			lba28_ok = lba_28_ok(block, n_block);
+		}
+
 		tf->flags |= ATA_TFLAG_LBA;
 
-		if (lba_28_ok(block, n_block)) {
+		if (lba28_ok) {
 			/* use LBA28 */
 			tf->device |= (block >> 24) & 0xf;
 		} else if (lba_48_ok(block, n_block)) {
@@ -742,9 +754,10 @@ 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;
-- 
2.37.3