From: David Milburn <dmilburn@redhat.com>
Date: Wed, 18 Aug 2010 23:59:40 -0400
Subject: [ata] sata_mv: warn on PIO with multiple DRQs
Message-id: <1282175987-21696-3-git-send-email-dmilburn@redhat.com>
Patchwork-id: 27689
O-Subject: [RHEL5.6 PATCH 2/9] BZ 554872 sata_mv: warn on PIO with multiple DRQs
Bugzilla: 554872
RH-Acked-by: Jeff Garzik <jgarzik@redhat.com>

commit c6112bd86bc8f727bb732a47f2133e0ff12beda9
Author: Mark Lord <liml@rtr.ca>
Date:   Wed Jun 18 12:13:02 2008 -0400

    sata_mv: warn on PIO with multiple DRQs

BZ 554872

diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index fe71321..f806333 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -1594,6 +1594,24 @@ static unsigned int mv_qc_issue(struct ata_queued_cmd *qc)
 
 	if ((qc->tf.protocol != ATA_PROT_DMA) &&
 	    (qc->tf.protocol != ATA_PROT_NCQ)) {
+		static int limit_warnings = 10;
+		/*
+		 * Errata SATA#16, SATA#24: warn if multiple DRQs expected.
+		 *
+		 * Someday, we might implement special polling workarounds
+		 * for these, but it all seems rather unnecessary since we
+		 * normally use only DMA for commands which transfer more
+		 * than a single block of data.
+		 *
+		 * Much of the time, this could just work regardless.
+		 * So for now, just log the incident, and allow the attempt.
+		 */
+		if (limit_warnings && (qc->nbytes / qc->sect_size) > 1) {
+			--limit_warnings;
+			ata_link_printk(qc->dev->link, KERN_WARNING, DRV_NAME
+					": attempting PIO w/multiple DRQ: "
+					"this may fail due to h/w errata\n");
+		}
 		/*
 		 * We're about to send a non-EDMA capable command to the
 		 * port.  Turn off EDMA so there won't be problems accessing