CentOS-5 patch: sata_via fix FIFO issue on vt6420/vt6421

CentOS bug #4864
Applied by Akemi Yagi <toracat@centos.org>
Adopted from ELRepo's kmod-sata_via patch.

2010-11-19     Tejun Heo    sata_via: apply magic FIFO fix to vt6420 too
2010-06-02     Tejun Heo    sata_via: magic vt6421 fix for transmission problems...
2010-06-07     Tejun Heo    sata_via: explain the magic fix

--- a/drivers/ata/sata_via.c.dist	2011-05-31 12:54:42.000000000 -0700
+++ a/drivers/ata/sata_via.c	2011-05-31 14:08:29.000000000 -0700
@@ -367,7 +367,7 @@
 	return 0;
 }
 
-static void svia_configure(struct pci_dev *pdev)
+static void svia_configure(struct pci_dev *pdev, int board_id)
 {
 	u8 tmp8;
 
@@ -404,6 +404,34 @@
 		tmp8 |= NATIVE_MODE_ALL;
 		pci_write_config_byte(pdev, SATA_NATIVE_MODE, tmp8);
 	}
+
+	/*
+	* vt6420/1 has problems talking to some drives.  The following
+	* is the fix from Joseph Chan <JosephChan@via.com.tw>.
+	*
+	* When host issues HOLD, device may send up to 20DW of data
+	* before acknowledging it with HOLDA and the host should be
+	* able to buffer them in FIFO.  Unfortunately, some WD drives
+	* send upto 40DW before acknowledging HOLD and, in the
+	* default configuration, this ends up overflowing vt6421's
+	* FIFO, making the controller abort the transaction with
+	* R_ERR.
+	*
+	* Rx52[2] is the internal 128DW FIFO Flow control watermark
+	* adjusting mechanism enable bit and the default value 0
+	* means host will issue HOLD to device when the left FIFO
+	* size goes below 32DW.  Setting it to 1 makes the watermark
+	* 64DW.
+	*
+	* https://bugzilla.kernel.org/show_bug.cgi?id=15173
+	* http://article.gmane.org/gmane.linux.ide/46352
+	* http://thread.gmane.org/gmane.linux.kernel/1062139
+	*/
+	if (board_id == vt6420 || board_id == vt6421) {
+		pci_read_config_byte(pdev, 0x52, &tmp8);
+		tmp8 |= 1 << 2;
+		pci_write_config_byte(pdev, 0x52, tmp8);
+	}
 }
 
 static int svia_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
@@ -445,7 +473,7 @@
 	if (rc)
 		return rc;
 
-	svia_configure(pdev);
+	svia_configure(pdev, board_id);
 
 	pci_set_master(pdev);
 	return ata_host_activate(host, pdev->irq, ata_sff_interrupt,