libata: Whitelist SSDs that are known to properly return zeroes after TRIM

As defined, the DRAT (Deterministic Read After Trim) and RZAT (Return
Zero After Trim) flags in the ATA Command Set are unreliable in the
sense that they only define what happens if the device successfully
executed the DSM TRIM command. TRIM is only advisory, however, and the
device is free to silently ignore all or parts of the request.

In practice this renders the DRAT and RZAT flags completely useless and
because the results are unpredictable we decided to disable discard in
MD for 3.18 to avoid the risk of data corruption.

Hardware vendors in the real world obviously need better guarantees than
what the standards bodies provide. Unfortuntely those guarantees are
encoded in product requirements documents rather than somewhere we can
key off of them programatically. So we are compelled to disabling
discard_zeroes_data for all devices unless we explicitly have data to
support whitelisting them.

This patch whitelists SSDs from a few of the main vendors. None of the
whitelists are based on written guarantees. They are purely based on
empirical evidence collected from internal and external users that have
tested or qualified these drives in RAID deployments.

The whitelist is only meant as a starting point and is by no means
comprehensive:

   - All intel SSD models except for 510
   - Micron M5?0/M600
   - Samsung SSDs
   - Seagate SSDs

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index e364e86e84d7..6abd17a85b13 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2532,13 +2532,15 @@ static unsigned int ata_scsiop_read_cap(struct ata_scsi_args *args, u8 *rbuf)
 		rbuf[15] = lowest_aligned;
 
 		if (ata_id_has_trim(args->id)) {
-			rbuf[14] |= 0x80; /* TPE */
+			rbuf[14] |= 0x80; /* LBPME */
 
-			if (ata_id_has_zero_after_trim(args->id))
-				rbuf[14] |= 0x40; /* TPRZ */
+			if (ata_id_has_zero_after_trim(args->id) &&
+			    dev->horkage & ATA_HORKAGE_ZERO_AFTER_TRIM) {
+				ata_dev_info(dev, "Enabling discard_zeroes_data\n");
+				rbuf[14] |= 0x40; /* LBPRZ */
+			}
 		}
 	}
-
 	return 0;
 }