From: Bhavana Nagendra <bnagendr@redhat.com>
Date: Tue, 1 Apr 2008 10:57:04 -0400
Subject: [sata] SB600: add 255-sector limit
Message-id: 47F24D40.9090201@redhat.com
O-Subject: Re: [RHEL5.2 PATCH] AMD SB700/SB800 SATA support 64bit DMA
Bugzilla: 434741

This is the commit list Jeff and I discussed:
 > 1) a long time ago: disable 64-bit DMA on SB600, etc:
c7a42156d99bcea7f8173ba7a6034bbaa2ecb77c
This patch is already in R5.2 code base.    I sent Jeff a collection of
7 submission with upstream commits
so he knows what AMD requested, tested and submitted so far.

 > 2) re-enable 64-bit DMA on SB700, SB800:
e39fc8c9fd0bb6f4018186801e4a53a5eccaaf70
This is the SB700/800 patch I originally submitted, call that patch 1.

 > 3) add 255-sector limit to SB600, erroneously remove 32-bit limit for
SB600: a878539ef994787c447a98c2e3ba0fe3dad984ec
 > 4) restore 32-bit limit removed in step #3, and improve diagnostic
output: 4cde32fc4b32e96a99063af3183acdfd54c563f0

These two commits are necessary in R5.2:

The attached patch addresses the AMD SB600 errata,  where the hardware does
not like 256-length PRD entries during FPDMA (aka NCQ).
It hurts performance
on SB600, but it is more important to get a
correct patch eliminating the data
corruption/lockups, and then later on tune for performance.
We simply limit each command to a maximum of 255 sectors, on SB600.

At least one report claims that a878539ef994787c447a98c2e3ba0fe3dad984ec
<http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=object;h=a878539ef994787c447a98c2e3ba0fe3dad984ec>
failed to solve lockups, whereas the old limit-to-32-bit trick worked.
Restore the 32-bit limit, but also leave the 255-sector limit in place,
because we know that's needed as well.

The attached patch is a back port of the two related upstream commits
combined.  I'm submitting the additional patch for review to make snapshot4
this week.  The brew build and RHEL RPM testing will be completed in the
next couple of days.

Thanks, if there are any issues let me know.

Please ACK for R5.2.

Bhavana

Acked-by: Jeff Garzik <jgarzik@redhat.com>

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index f11bdbf..a267120 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -186,6 +186,7 @@ enum {
 	AHCI_HFLAG_NO_MSI		= (1 << 5), /* no PCI MSI */
 	AHCI_HFLAG_NO_PMP		= (1 << 6), /* no PMP */
 	AHCI_HFLAG_NO_HOTPLUG		= (1 << 7), /* ignore PxSERR.DIAG.N */
+	AHCI_HFLAG_SECT255              = (1 << 8), /* max 255 sectors */
 
 	/* ap->flags bits */
 
@@ -255,6 +256,7 @@ static void ahci_vt8251_error_handler(struct ata_port *ap);
 static void ahci_p5wdh_error_handler(struct ata_port *ap);
 static void ahci_post_internal_cmd(struct ata_queued_cmd *qc);
 static int ahci_port_resume(struct ata_port *ap);
+static void ahci_dev_config(struct ata_device *dev);
 static unsigned int ahci_fill_sg(struct ata_queued_cmd *qc, void *cmd_tbl);
 static void ahci_fill_cmd_slot(struct ahci_port_priv *pp, unsigned int tag,
 			       u32 opts);
@@ -294,6 +296,8 @@ static const struct ata_port_operations ahci_ops = {
 	.check_altstatus	= ahci_check_status,
 	.dev_select		= ata_noop_dev_select,
 
+	.dev_config             = ahci_dev_config,
+
 	.tf_read		= ahci_tf_read,
 
 	.qc_defer		= sata_pmp_qc_defer_cmd_switch,
@@ -425,7 +429,8 @@ static const struct ata_port_info ahci_port_info[] = {
 	/* board_ahci_sb600 */
 	{
 		AHCI_HFLAGS	(AHCI_HFLAG_IGN_SERR_INTERNAL |
-				 AHCI_HFLAG_32BIT_ONLY | AHCI_HFLAG_NO_PMP),
+				 AHCI_HFLAG_32BIT_ONLY |
+				 AHCI_HFLAG_SECT255 | AHCI_HFLAG_NO_PMP), 
 		.flags		= AHCI_FLAG_COMMON,
 		.link_flags	= AHCI_LFLAG_COMMON,
 		.pio_mask	= 0x1f, /* pio0-4 */
@@ -1164,6 +1169,17 @@ static void ahci_init_controller(struct ata_host *host)
 	VPRINTK("HOST_CTL 0x%x\n", tmp);
 }
 
+static void ahci_dev_config(struct ata_device *dev)
+{
+	struct ahci_host_priv *hpriv = dev->link->ap->host->private_data;
+
+	if (hpriv->flags & AHCI_HFLAG_SECT255) {
+		dev->max_sectors = 255;
+		ata_dev_printk(dev, KERN_INFO,
+				"SB600 AHCI: limiting to 255 sectors per cmd\n");
+	}
+}
+
 static unsigned int ahci_dev_classify(struct ata_port *ap)
 {
 	void __iomem *port_mmio = ahci_port_base(ap);