sata_sis: SCR accessors return -EINVAL when requested SCR isn't available

sis_scr_cfg_read() can't access SError and was incorrectly returning
-1 instead of -EINVAL.  This went unnoticed because SError used to be
cleared in @postreset() and it didn't care about how scr_read() failed
but commit ac371987 moved SError clearing into sata_link_resume() and
SCR access failure other than -EINVAL is considered an error condition
and exposes the incorrect return value bug as detection failure.  Fix
it.

Also, scsi_scr_cfg_write() was incorrectly returning 0 after it
ignored the request to write to SError.  Make it also return -EINVAL.

This was bisected and reported by Patrick McHardy.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_sis.c

@@ -142,7 +142,7 @@ static u32 sis_scr_cfg_read(struct ata_port *ap, unsigned int sc_reg, u32 *val)
 	u8 pmr;
 
 	if (sc_reg == SCR_ERROR) /* doesn't exist in PCI cfg space */
-		return 0xffffffff;
+		return -EINVAL;
 
 	pci_read_config_byte(pdev, SIS_PMR, &pmr);
 
@@ -158,14 +158,14 @@ static u32 sis_scr_cfg_read(struct ata_port *ap, unsigned int sc_reg, u32 *val)
 	return 0;
 }
 
-static void sis_scr_cfg_write(struct ata_port *ap, unsigned int sc_reg, u32 val)
+static int sis_scr_cfg_write(struct ata_port *ap, unsigned int sc_reg, u32 val)
 {
 	struct pci_dev *pdev = to_pci_dev(ap->host->dev);
 	unsigned int cfg_addr = get_scr_cfg_addr(ap, sc_reg);
 	u8 pmr;
 
 	if (sc_reg == SCR_ERROR) /* doesn't exist in PCI cfg space */
-		return;
+		return -EINVAL;
 
 	pci_read_config_byte(pdev, SIS_PMR, &pmr);
 
@@ -174,6 +174,8 @@ static void sis_scr_cfg_write(struct ata_port *ap, unsigned int sc_reg, u32 val)
 	if ((pdev->device == 0x0182) || (pdev->device == 0x0183) ||
 	    (pdev->device == 0x1182) || (pmr & SIS_PMR_COMBINED))
 		pci_write_config_dword(pdev, cfg_addr+0x10, val);
+
+	return 0;
 }
 
 static int sis_scr_read(struct ata_port *ap, unsigned int sc_reg, u32 *val)
@@ -211,14 +213,14 @@ static int sis_scr_write(struct ata_port *ap, unsigned int sc_reg, u32 val)
 	pci_read_config_byte(pdev, SIS_PMR, &pmr);
 
 	if (ap->flags & SIS_FLAG_CFGSCR)
-		sis_scr_cfg_write(ap, sc_reg, val);
+		return sis_scr_cfg_write(ap, sc_reg, val);
 	else {
 		iowrite32(val, ap->ioaddr.scr_addr + (sc_reg * 4));
 		if ((pdev->device == 0x0182) || (pdev->device == 0x0183) ||
 		    (pdev->device == 0x1182) || (pmr & SIS_PMR_COMBINED))
 			iowrite32(val, ap->ioaddr.scr_addr + (sc_reg * 4)+0x10);
+		return 0;
 	}
-	return 0;
 }
 
 static int sis_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)