[PATCH] fix ServerWorks PIO auto-tuning

If PIO mode should be auto-tuned xferspeed argument for svwks_tune_chipset()
is equal to 255 (0xFF).  It is then passed to ide_rate_filter() which matches
desired mode with chipset capabilities.  Since 255 is greater than any of the
values used for transfer modes, ide_rate_filter() will always return the
highest mode supported by both device/chipset (which sometimes should not be
used ie. when host is a simplex one) and the wrong mode will be set.

Thanks to Torben Mathiasen and Tomas Szepe for testing it.

drivers/ide/pci/serverworks.c

@@ -272,7 +272,7 @@ static int svwks_tune_chipset (ide_drive_t *drive, u8 xferspeed)
 
 	ide_hwif_t *hwif	= HWIF(drive);
 	struct pci_dev *dev	= hwif->pci_dev;
-	u8 speed		= ide_rate_filter(svwks_ratemask(drive), xferspeed);
+	u8 speed;
 	u8 pio			= ide_get_best_pio_mode(drive, 255, 5, NULL);
 	u8 unit			= (drive->select.b.unit & 0x01);
 	u8 csb5			= svwks_csb_check(dev);
@@ -280,6 +280,11 @@ static int svwks_tune_chipset (ide_drive_t *drive, u8 xferspeed)
 	u8 dma_timing		= 0, pio_timing = 0;
 	u16 csb5_pio		= 0;
 
+	if (xferspeed == 255)	/* PIO auto-tuning */
+		speed = XFER_PIO_0 + pio;
+	else
+		speed = ide_rate_filter(svwks_ratemask(drive), xferspeed);
+
 	/* If we are about to put a disk into UDMA mode we screwed up.
 	   Our code assumes we never _ever_ do this on an OSB4 */