libata: fix ata_acpi_gtm_xfermask()

ata_acpi_gtm_xfermask() as separated out from pacpi_discover_modes()
has various bugs.  Fix them.

* The wrong comparison operator is used when finding for matching
  cycle resulting totally bogus result.

* With the comparion operator fixed, boundary condtion handling is
  clumsy.

* Setting of any DMA mask bit set all bits in PIO mask.

* MWDMA and UDMA blocks are swapped.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-acpi.c

@@ -473,49 +473,49 @@ EXPORT_SYMBOL_GPL(ata_acpi_udma_cycle);
 unsigned long ata_acpi_gtm_xfermask(struct ata_device *dev,
 				    const struct ata_acpi_gtm *gtm)
 {
+	unsigned long pio_mask = 0, mwdma_mask = 0, udma_mask = 0;
 	int unit, i;
 	u32 t;
-	unsigned long mask = (0x7f << ATA_SHIFT_UDMA) | (0x7 << ATA_SHIFT_MWDMA) | (0x1F << ATA_SHIFT_PIO);
 
 	/* we always use the 0 slot for crap hardware */
 	unit = dev->devno;
 	if (!(gtm->flags & 0x10))
 		unit = 0;
 
+	/* Values larger than the longest cycle results in 0 mask
+	 * while values equal to smaller than the shortest cycle
+	 * results in mask which includes all supported modes.
+	 * Disabled transfer method has the value of 0xffffffff which
+	 * will always result in 0 mask.
+	 */
+
 	/* start by scanning for PIO modes */
-	for (i = 0; i < 7; i++) {
-		t = gtm->drive[unit].pio;
-		if (t <= ata_acpi_pio_cycle[i]) {
-			mask |= (2 << (ATA_SHIFT_PIO + i)) - 1;
+	t = gtm->drive[unit].pio;
+	for (i = 0; i < ARRAY_SIZE(ata_acpi_pio_cycle); i++)
+		if (t > ata_acpi_pio_cycle[i])
 			break;
-		}
-	}
+	pio_mask = (1 << i) - 1;
 
 	/* See if we have MWDMA or UDMA data. We don't bother with
 	 * MWDMA if UDMA is available as this means the BIOS set UDMA
 	 * and our error changedown if it works is UDMA to PIO anyway.
 	 */
-	if (gtm->flags & (1 << (2 * unit))) {
+	t = gtm->drive[unit].dma;
+	if (!(gtm->flags & (1 << (2 * unit)))) {
 		/* MWDMA */
-		for (i = 0; i < 5; i++) {
-			t = gtm->drive[unit].dma;
-			if (t <= ata_acpi_mwdma_cycle[i]) {
-				mask |= (2 << (ATA_SHIFT_MWDMA + i)) - 1;
+		for (i = 0; i < ARRAY_SIZE(ata_acpi_mwdma_cycle); i++)
+			if (t > ata_acpi_mwdma_cycle[i])
 				break;
-			}
-		}
+		mwdma_mask = (1 << i) - 1;
 	} else {
 		/* UDMA */
-		for (i = 0; i < 7; i++) {
-			t = gtm->drive[unit].dma;
-			if (t <= ata_acpi_udma_cycle[i]) {
-				mask |= (2 << (ATA_SHIFT_UDMA + i)) - 1;
+		for (i = 0; i < ARRAY_SIZE(ata_acpi_udma_cycle); i++)
+			if (t > ata_acpi_udma_cycle[i])
 				break;
-			}
-		}
+		udma_mask = (1 << i) - 1;
 	}
 
-	return mask;
+	return ata_pack_xfermask(pio_mask, mwdma_mask, udma_mask);
 }
 EXPORT_SYMBOL_GPL(ata_acpi_gtm_xfermask);