[PATCH] sata_via: use old SCR access pattern on vt6420

vt6420 has super-fragile SCR registers which can hang the whole
machine if accessed with the wrong timings.  This patch makes sata_via
use SCR registers only during probing and with the same timings as
before (pre new EH), which is proven to work.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/scsi/sata_via.c

@@ -74,6 +74,7 @@ enum {
 static int svia_init_one (struct pci_dev *pdev, const struct pci_device_id *ent);
 static u32 svia_scr_read (struct ata_port *ap, unsigned int sc_reg);
 static void svia_scr_write (struct ata_port *ap, unsigned int sc_reg, u32 val);
+static void vt6420_error_handler(struct ata_port *ap);
 
 static const struct pci_device_id svia_pci_tbl[] = {
 	{ 0x1106, 0x3149, PCI_ANY_ID, PCI_ANY_ID, 0, 0, vt6420 },
@@ -107,7 +108,38 @@ static struct scsi_host_template svia_sht = {
 	.bios_param		= ata_std_bios_param,
 };
 
-static const struct ata_port_operations svia_sata_ops = {
+static const struct ata_port_operations vt6420_sata_ops = {
+	.port_disable		= ata_port_disable,
+
+	.tf_load		= ata_tf_load,
+	.tf_read		= ata_tf_read,
+	.check_status		= ata_check_status,
+	.exec_command		= ata_exec_command,
+	.dev_select		= ata_std_dev_select,
+
+	.bmdma_setup            = ata_bmdma_setup,
+	.bmdma_start            = ata_bmdma_start,
+	.bmdma_stop		= ata_bmdma_stop,
+	.bmdma_status		= ata_bmdma_status,
+
+	.qc_prep		= ata_qc_prep,
+	.qc_issue		= ata_qc_issue_prot,
+	.data_xfer		= ata_pio_data_xfer,
+
+	.freeze			= ata_bmdma_freeze,
+	.thaw			= ata_bmdma_thaw,
+	.error_handler		= vt6420_error_handler,
+	.post_internal_cmd	= ata_bmdma_post_internal_cmd,
+
+	.irq_handler		= ata_interrupt,
+	.irq_clear		= ata_bmdma_irq_clear,
+
+	.port_start		= ata_port_start,
+	.port_stop		= ata_port_stop,
+	.host_stop		= ata_host_stop,
+};
+
+static const struct ata_port_operations vt6421_sata_ops = {
 	.port_disable		= ata_port_disable,
 
 	.tf_load		= ata_tf_load,
@@ -141,13 +173,13 @@ static const struct ata_port_operations svia_sata_ops = {
 	.host_stop		= ata_host_stop,
 };
 
-static struct ata_port_info svia_port_info = {
+static struct ata_port_info vt6420_port_info = {
 	.sht		= &svia_sht,
 	.host_flags	= ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY,
 	.pio_mask	= 0x1f,
 	.mwdma_mask	= 0x07,
 	.udma_mask	= 0x7f,
-	.port_ops	= &svia_sata_ops,
+	.port_ops	= &vt6420_sata_ops,
 };
 
 MODULE_AUTHOR("Jeff Garzik");
@@ -170,6 +202,81 @@ static void svia_scr_write (struct ata_port *ap, unsigned int sc_reg, u32 val)
 	outl(val, ap->ioaddr.scr_addr + (4 * sc_reg));
 }
 
+/**
+ *	vt6420_prereset - prereset for vt6420
+ *	@ap: target ATA port
+ *
+ *	SCR registers on vt6420 are pieces of shit and may hang the
+ *	whole machine completely if accessed with the wrong timing.
+ *	To avoid such catastrophe, vt6420 doesn't provide generic SCR
+ *	access operations, but uses SStatus and SControl only during
+ *	boot probing in controlled way.
+ *
+ *	As the old (pre EH update) probing code is proven to work, we
+ *	strictly follow the access pattern.
+ *
+ *	LOCKING:
+ *	Kernel thread context (may sleep)
+ *
+ *	RETURNS:
+ *	0 on success, -errno otherwise.
+ */
+static int vt6420_prereset(struct ata_port *ap)
+{
+	struct ata_eh_context *ehc = &ap->eh_context;
+	unsigned long timeout = jiffies + (HZ * 5);
+	u32 sstatus, scontrol;
+	int online;
+
+	/* don't do any SCR stuff if we're not loading */
+	if (!ATA_PFLAG_LOADING)
+		goto skip_scr;
+
+	/* Resume phy.  This is the old resume sequence from
+	 * __sata_phy_reset().
+	 */
+	svia_scr_write(ap, SCR_CONTROL, 0x300);
+	svia_scr_read(ap, SCR_CONTROL); /* flush */
+
+	/* wait for phy to become ready, if necessary */
+	do {
+		msleep(200);
+		if ((svia_scr_read(ap, SCR_STATUS) & 0xf) != 1)
+			break;
+	} while (time_before(jiffies, timeout));
+
+	/* open code sata_print_link_status() */
+	sstatus = svia_scr_read(ap, SCR_STATUS);
+	scontrol = svia_scr_read(ap, SCR_CONTROL);
+
+	online = (sstatus & 0xf) == 0x3;
+
+	ata_port_printk(ap, KERN_INFO,
+			"SATA link %s 1.5 Gbps (SStatus %X SControl %X)\n",
+			online ? "up" : "down", sstatus, scontrol);
+
+	/* SStatus is read one more time */
+	svia_scr_read(ap, SCR_STATUS);
+
+	if (!online) {
+		/* tell EH to bail */
+		ehc->i.action &= ~ATA_EH_RESET_MASK;
+		return 0;
+	}
+
+ skip_scr:
+	/* wait for !BSY */
+	ata_busy_sleep(ap, ATA_TMOUT_BOOT_QUICK, ATA_TMOUT_BOOT);
+
+	return 0;
+}
+
+static void vt6420_error_handler(struct ata_port *ap)
+{
+	return ata_bmdma_drive_eh(ap, vt6420_prereset, ata_std_softreset,
+				  NULL, ata_std_postreset);
+}
+
 static const unsigned int svia_bar_sizes[] = {
 	8, 4, 8, 4, 16, 256
 };
@@ -210,7 +317,7 @@ static void vt6421_init_addrs(struct ata_probe_ent *probe_ent,
 static struct ata_probe_ent *vt6420_init_probe_ent(struct pci_dev *pdev)
 {
 	struct ata_probe_ent *probe_ent;
-	struct ata_port_info *ppi = &svia_port_info;
+	struct ata_port_info *ppi = &vt6420_port_info;
 
 	probe_ent = ata_pci_init_native_mode(pdev, &ppi, ATA_PORT_PRIMARY | ATA_PORT_SECONDARY);
 	if (!probe_ent)
@@ -239,7 +346,7 @@ static struct ata_probe_ent *vt6421_init_probe_ent(struct pci_dev *pdev)
 
 	probe_ent->sht		= &svia_sht;
 	probe_ent->host_flags	= ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY;
-	probe_ent->port_ops	= &svia_sata_ops;
+	probe_ent->port_ops	= &vt6421_sata_ops;
 	probe_ent->n_ports	= N_PORTS;
 	probe_ent->irq		= pdev->irq;
 	probe_ent->irq_flags	= IRQF_SHARED;