usb: phy-msm-ssusb-qmp: Make vls_clamp_reg as optional

Currently the SSUSB QMP PHY driver mandates that vls_clamp_reg be
passed from the DTSI. But this register cannot be accessed on a
platform on which Linux is a guest OS. This can lead to errors
when trying to enable autonomous mode. Work around this situation
by making the vls_clamp_reg property as optional.

Change-Id: Idb103d9b7bda717a5f12689951a7452c46aa76dd
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>

Documentation/devicetree/bindings/usb/msm-phy.txt

@@ -95,8 +95,6 @@ Required properties:
  - reg: Address and length of the register set for the device
    Required regs are:
    "qmp_phy_base" : QMP PHY Base register set.
- - "vls_clamp_reg" : top-level CSR register to be written to enable phy vls
-   clamp which allows phy to detect autonomous mode.
  - <supply-name>-supply: phandle to the regulator device tree node
    Required "supply-name" examples are:
 	"vdd" : vdd supply for SSPHY digital circuit operation
@@ -125,6 +123,8 @@ Required properties:
 
 Optional properties:
  - reg: Additional register set of address and length to control QMP PHY are:
+   "vls_clamp_reg" : top-level CSR register to be written to enable phy vls
+   clamp which allows phy to detect autonomous mode.
    "tcsr_usb3_dp_phymode" : top-level CSR register to be written to select
    super speed usb qmp phy.
  - clocks: a list of phandles to the PHY clocks. Use as per

drivers/usb/phy/phy-msm-ssusb-qmp.c

@@ -473,11 +473,13 @@ static int msm_ssphy_qmp_set_suspend(struct usb_phy *uphy, int suspend)
 	}
 
 	if (suspend) {
-		if (phy->cable_connected)
-			msm_ssusb_qmp_enable_autonomous(phy, 1);
-		else
+		if (phy->cable_connected) {
+			if (phy->vls_clamp_reg)
+				msm_ssusb_qmp_enable_autonomous(phy, 1);
+		} else {
 			writel_relaxed(0x00,
 			phy->base + phy->phy_reg[USB3_PHY_POWER_DOWN_CONTROL]);
+		}
 
 		/* Make sure above write completed with PHY */
 		wmb();
@@ -509,7 +511,8 @@ static int msm_ssphy_qmp_set_suspend(struct usb_phy *uphy, int suspend)
 			writel_relaxed(0x01,
 			phy->base + phy->phy_reg[USB3_PHY_POWER_DOWN_CONTROL]);
 		} else  {
-			msm_ssusb_qmp_enable_autonomous(phy, 0);
+			if (phy->vls_clamp_reg)
+				msm_ssusb_qmp_enable_autonomous(phy, 0);
 		}
 
 		/* Make sure that above write completed with PHY */
@@ -648,13 +651,13 @@ static int msm_ssphy_qmp_probe(struct platform_device *pdev)
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM,
 			"vls_clamp_reg");
 	if (!res) {
-		dev_err(dev, "failed getting vls_clamp_reg\n");
-		return -ENODEV;
-	}
-	phy->vls_clamp_reg = devm_ioremap_resource(dev, res);
-	if (IS_ERR(phy->vls_clamp_reg)) {
-		dev_err(dev, "couldn't find vls_clamp_reg address.\n");
-		return PTR_ERR(phy->vls_clamp_reg);
+		dev_dbg(dev, "vls_clamp_reg not passed\n");
+	} else {
+		phy->vls_clamp_reg = devm_ioremap_resource(dev, res);
+		if (IS_ERR(phy->vls_clamp_reg)) {
+			dev_err(dev, "couldn't find vls_clamp_reg address.\n");
+			return PTR_ERR(phy->vls_clamp_reg);
+		}
 	}
 
 	res = platform_get_resource_byname(pdev, IORESOURCE_MEM,