Some revisions of the Serverworks K2 SATA controller have a data

corruption bug where if an ATA command is issued before DMA is started,
data will become available to the controller before it knows what to do
with it. This results in either data corruption or a controller crash.

This patch remedies the problem by adopting the workaround employed
by Linux and Darwin: starting the DMA engine prior to sending the ATA
command.

Observer on:	Xserve G5
Reviewed by:	mav
MFC after:	1 week

3 files changed, 21 insertions, 1 deletions

diff --git a/sys/dev/ata/ata-all.h b/sys/dev/ata/ata-all.h
index d7b3f4412d60..336f0e3966e0 100644
--- a/sys/dev/ata/ata-all.h
+++ b/sys/dev/ata/ata-all.h
@@ -564,6 +564,7 @@ struct ata_channel {
 #define         ATA_CHECKS_CABLE	0x20
 #define         ATA_NO_ATAPI_DMA	0x40
 #define         ATA_SATA		0x80
+#define         ATA_DMA_BEFORE_CMD	0x100
 
     int				pm_level;	/* power management level */
     int                         devices;        /* what is present */
diff --git a/sys/dev/ata/ata-lowlevel.c b/sys/dev/ata/ata-lowlevel.c
index 566b8f676a59..6c196d60a442 100644
--- a/sys/dev/ata/ata-lowlevel.c
+++ b/sys/dev/ata/ata-lowlevel.c
@@ -141,6 +141,14 @@ ata_begin_transaction(struct ata_request *request)
 	    goto begin_finished;
 	}
 
+	/* start DMA engine if necessary */
+	if ((ch->flags & ATA_DMA_BEFORE_CMD) &&
+	   ch->dma.start && ch->dma.start(request)) {
+	    device_printf(request->parent, "error starting DMA\n");
+	    request->result = EIO;
+	    goto begin_finished;
+	}
+
 	/* issue command */
 	if (ch->hw.command(request)) {
 	    device_printf(request->parent, "error issuing %s command\n",
@@ -150,7 +158,8 @@ ata_begin_transaction(struct ata_request *request)
 	}
 
 	/* start DMA engine */
-	if (ch->dma.start && ch->dma.start(request)) {
+	if (!(ch->flags & ATA_DMA_BEFORE_CMD) &&
+	   ch->dma.start && ch->dma.start(request)) {
 	    device_printf(request->parent, "error starting DMA\n");
 	    request->result = EIO;
 	    goto begin_finished;
diff --git a/sys/dev/ata/chipsets/ata-serverworks.c b/sys/dev/ata/chipsets/ata-serverworks.c
index 29718ec5e48b..cee56e3681ee 100644
--- a/sys/dev/ata/chipsets/ata-serverworks.c
+++ b/sys/dev/ata/chipsets/ata-serverworks.c
@@ -241,6 +241,16 @@ ata_serverworks_ch_attach(device_t dev)
 	ATA_OUTL(ctlr->r_res2, ch_offset + 0x88, 0);
 	ATA_OUTL(ctlr->r_res2, ch_offset + 0x80,
 	    ATA_INL(ctlr->r_res2, ch_offset + 0x80) & ~0x00040000);
+
+	/*
+	 * Some controllers have a bug where they will send the command
+	 * to the drive before seeing a DMA start, and then can begin
+	 * receiving data before the DMA start arrives. The controller
+	 * will then become confused and either corrupt the data or crash.
+	 * Remedy this by starting DMA before sending the drive command.
+	 */
+
+	ch->flags |= ATA_DMA_BEFORE_CMD;
     }
 
     /* chip does not reliably do 64K DMA transfers */