From: Sergei Shtylyov <sshtylyov@ru.mvista.com>

ide_dma_speed() fails to actually honor the IDE drivers' mode support
masks) because of the bogus checks -- thus, selecting the DMA transfer mode
that the driver explicitly refuses to support is possible.  Additionally,
there is no check for validity of the UltraDMA mode data in the drive ID,
and the function is misdocumented.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 drivers/ide/ide-lib.c |  125 +++++++++++++++++++++++-----------------
 1 file changed, 73 insertions(+), 52 deletions(-)

diff -puN drivers/ide/ide-lib.c~ide_dma_speed-fixes drivers/ide/ide-lib.c
--- a/drivers/ide/ide-lib.c~ide_dma_speed-fixes
+++ a/drivers/ide/ide-lib.c
@@ -72,75 +72,96 @@ EXPORT_SYMBOL(ide_xfer_verbose);
 /**
  *	ide_dma_speed	-	compute DMA speed
  *	@drive: drive
- *	@mode; intended mode
+ *	@mode:	modes available
  *
  *	Checks the drive capabilities and returns the speed to use
- *	for the transfer. Returns -1 if the requested mode is unknown
- *	(eg PIO)
+ *	for the DMA transfer.  Returns 0 if the drive is incapable
+ *	of DMA transfers.
  */
  
 u8 ide_dma_speed(ide_drive_t *drive, u8 mode)
 {
 	struct hd_driveid *id   = drive->id;
 	ide_hwif_t *hwif	= HWIF(drive);
+	u8 ultra_mask, mwdma_mask, swdma_mask;
 	u8 speed = 0;
 
 	if (drive->media != ide_disk && hwif->atapi_dma == 0)
 		return 0;
 
-	switch(mode) {
-		case 0x04:
-			if ((id->dma_ultra & 0x0040) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_6; break; }
-		case 0x03:
-			if ((id->dma_ultra & 0x0020) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_5; break; }
-		case 0x02:
-			if ((id->dma_ultra & 0x0010) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_4; break; }
-			if ((id->dma_ultra & 0x0008) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_3; break; }
-		case 0x01:
-			if ((id->dma_ultra & 0x0004) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_2; break; }
-			if ((id->dma_ultra & 0x0002) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_1; break; }
-			if ((id->dma_ultra & 0x0001) &&
-			    (id->dma_ultra & hwif->ultra_mask))
-				{ speed = XFER_UDMA_0; break; }
-		case 0x00:
-			if ((id->dma_mword & 0x0004) &&
-			    (id->dma_mword & hwif->mwdma_mask))
-				{ speed = XFER_MW_DMA_2; break; }
-			if ((id->dma_mword & 0x0002) &&
-			    (id->dma_mword & hwif->mwdma_mask))
-				{ speed = XFER_MW_DMA_1; break; }
-			if ((id->dma_mword & 0x0001) &&
-			    (id->dma_mword & hwif->mwdma_mask))
-				{ speed = XFER_MW_DMA_0; break; }
-			if ((id->dma_1word & 0x0004) &&
-			    (id->dma_1word & hwif->swdma_mask))
-				{ speed = XFER_SW_DMA_2; break; }
-			if ((id->dma_1word & 0x0002) &&
-			    (id->dma_1word & hwif->swdma_mask))
-				{ speed = XFER_SW_DMA_1; break; }
-			if ((id->dma_1word & 0x0001) &&
-			    (id->dma_1word & hwif->swdma_mask))
-				{ speed = XFER_SW_DMA_0; break; }
-	}
+	/* Capable of UltraDMA modes? */
+	ultra_mask = id->dma_ultra & hwif->ultra_mask;
+
+	if (!(id->field_valid & 4))
+		mode = 0;	/* fallback to MW/SW DMA if no UltraDMA */
+
+	switch (mode) {
+	case 4:
+		if (ultra_mask & 0x40) {
+			speed = XFER_UDMA_6;
+			break;
+		}
+	case 3:
+		if (ultra_mask & 0x20) {
+			speed = XFER_UDMA_5;
+			break;
+		}
+	case 2:
+		if (ultra_mask & 0x10) {
+			speed = XFER_UDMA_4;
+			break;
+		}
+		if (ultra_mask & 0x08) {
+			speed = XFER_UDMA_3;
+			break;
+		}
+	case 1:
+		if (ultra_mask & 0x04) {
+			speed = XFER_UDMA_2;
+			break;
+		}
+		if (ultra_mask & 0x02) {
+			speed = XFER_UDMA_1;
+			break;
+		}
+		if (ultra_mask & 0x01) {
+			speed = XFER_UDMA_0;
+			break;
+		}
+	case 0:
+		mwdma_mask = id->dma_mword & hwif->mwdma_mask;
 
-//	printk("%s: %s: mode 0x%02x, speed 0x%02x\n",
-//		__FUNCTION__, drive->name, mode, speed);
+		if (mwdma_mask & 0x04) {
+			speed = XFER_MW_DMA_2;
+			break;
+		}
+		if (mwdma_mask & 0x02) {
+			speed = XFER_MW_DMA_1;
+			break;
+		}
+		if (mwdma_mask & 0x01) {
+			speed = XFER_MW_DMA_0;
+			break;
+		}
+
+		swdma_mask = id->dma_1word & hwif->swdma_mask;
+
+		if (swdma_mask & 0x04) {
+			speed = XFER_SW_DMA_2;
+			break;
+		}
+		if (swdma_mask & 0x02) {
+			speed = XFER_SW_DMA_1;
+			break;
+		}
+		if (swdma_mask & 0x01) {
+			speed = XFER_SW_DMA_0;
+			break;
+		}
+	}
 
 	return speed;
 }
-
 EXPORT_SYMBOL(ide_dma_speed);
 
 
_