pinctrl: intel: check REVID register value for device presence

Use the value read from the REVID register in order to check for the
presence of the device. A read of all ones is treated as if the device
is not present, and hence probing is ended.

This fixes an issue when running as a Xen PVH dom0, where the ACPI
DSDT table is provided unmodified to dom0 and hence contains the
pinctrl devices, but the MMIO region(s) containing the device
registers might not be mapped in the guest physical memory map if such
region(s) are not exposed on a PCI device BAR or marked as reserved in
the host memory map.

Fixes: 91d898e5 ("pinctrl: intel: Convert capability list to features")
Suggested-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/pinctrl/intel/pinctrl-intel.c

@@ -1493,8 +1493,13 @@ static int intel_pinctrl_probe(struct platform_device *pdev,
 		if (IS_ERR(regs))
 			return PTR_ERR(regs);
 
-		/* Determine community features based on the revision */
+		/*
+		 * Determine community features based on the revision.
+		 * A value of all ones means the device is not present.
+		 */
 		value = readl(regs + REVID);
+		if (value == ~0u)
+			return -ENODEV;
 		if (((value & REVID_MASK) >> REVID_SHIFT) >= 0x94) {
 			community->features |= PINCTRL_FEATURE_DEBOUNCE;
 			community->features |= PINCTRL_FEATURE_1K_PD;