[PATCH] ide tcq fixes

This fixes a few problems with ide tcq, I don't know of any other known
ones (and it is solid here, survives ours of beating on it). Basically:

- Don't enable tcq if the drive isn't alone on the channel. This raises
  all sorts of fun that really requires hardware support (auto poll), or
  it's going to _suck_. I never wanted to do that, and no hardware I
  know of supports auto-poll.

- Introduce a drive blacklist so we don't enable tcq on known broken
  drives. Or enable with restrictions on some models.

- Add a check for pdc4030, apparently tcq doesn't work there (hell knows
  who would be crazy enough to pull such a stunt).

drivers/ide/ide-tcq.c

@@ -51,9 +51,58 @@
  */
 #undef IDE_TCQ_FIDDLE_SI
 
+/*
+ * bad drive blacklist, for drives that raport tcq capability but don't
+ * work reliably with the default config. initially from freebsd table.
+ */
+struct ide_tcq_blacklist {
+	char *model;
+	char works;
+	unsigned int max_sectors;
+};
+
+static struct ide_tcq_blacklist ide_tcq_blacklist[] = {
+	{
+		.model =	"IBM-DTTA",
+		.works =	1,
+		.max_sectors =	128,
+	},
+	{
+		.model =	"IBM-DJNA",
+		.works =	0,
+	},
+	{
+		.model =	"WDC AC",
+		.works = 	0,
+	},
+	{
+		.model =	NULL,
+	},
+};
+
 ide_startstop_t ide_dmaq_intr(ide_drive_t *drive);
 ide_startstop_t ide_service(ide_drive_t *drive);
 
+static struct ide_tcq_blacklist *ide_find_drive_blacklist(ide_drive_t *drive)
+{
+	struct ide_tcq_blacklist *itb;
+	int i = 0;
+
+	do {
+		itb = &ide_tcq_blacklist[i];
+
+		if (!itb->model)
+			break;
+
+		if (!strncmp(drive->id->model, itb->model, strlen(itb->model)))
+			return itb;
+
+		i++;
+	} while (1);
+
+	return NULL;
+}
+
 static inline void drive_ctl_nien(ide_drive_t *drive, int set)
 {
 #ifdef IDE_TCQ_NIEN
@@ -502,7 +551,7 @@ static int ide_tcq_configure(ide_drive_t *drive)
 	return 0;
 err:
 	kfree(args);
-	return 1;
+	return -EIO;
 }
 
 /*
@@ -511,6 +560,7 @@ static int ide_tcq_configure(ide_drive_t *drive)
  */
 static int ide_enable_queued(ide_drive_t *drive, int on)
 {
+	struct ide_tcq_blacklist *itb;
 	int depth = drive->using_tcq ? drive->queue_depth : 0;
 
 	/*
@@ -529,6 +579,17 @@ static int ide_enable_queued(ide_drive_t *drive, int on)
 		return 1;
 	}
 
+	/*
+	 * some drives need limited transfer size in tcq
+	 */
+	itb = ide_find_drive_blacklist(drive);
+	if (itb && itb->max_sectors) {
+		if (itb->max_sectors > HWIF(drive)->rqsize)
+			itb->max_sectors = HWIF(drive)->rqsize;
+
+		blk_queue_max_sectors(&drive->queue, itb->max_sectors);
+	}
+
 	/*
 	 * enable block tagging
 	 */
@@ -582,13 +643,36 @@ int ide_tcq_wait_dataphase(ide_drive_t *drive)
 	return 0;
 }
 
+static int ide_tcq_check_blacklist(ide_drive_t *drive)
+{
+	struct ide_tcq_blacklist *itb = ide_find_drive_blacklist(drive);
+
+	if (!itb)
+		return 0;
+
+	return !itb->works;
+}
+
 int __ide_dma_queued_on(ide_drive_t *drive)
 {
 	if (!drive->using_dma)
 		return 1;
+	if (HWIF(drive)->chipset == ide_pdc4030)
+		return 1;
+	if (ide_tcq_check_blacklist(drive)) {
+		printk(KERN_WARNING "%s: tcq forbidden by blacklist\n",
+					drive->name);
+		return 1;
+	}
+	if (drive->next != drive) {
+		printk(KERN_WARNING "%s: only one drive on a channel supported"
+					" for tcq\n", drive->name);
+		return 1;
+	}
 
 	if (ata_pending_commands(drive)) {
-		printk(KERN_WARNING "ide-tcq; can't toggle tcq feature on busy drive\n");
+		printk(KERN_WARNING "ide-tcq; can't toggle tcq feature on "
+					"busy drive\n");
 		return 1;
 	}