[PATCH v3] intel/pinctrl: check REVID register value for device presence

[Roger Pau Monne <roger.pau@citrix.com>]

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.

91d898e51e60 ('pinctrl: intel: Convert capability list to features')
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v2:
 - Return ENODEV.
 - Adjust code comment.

Changes since v1:
 - New in this version.
---
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
---
 drivers/pinctrl/intel/pinctrl-intel.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/pinctrl/intel/pinctrl-intel.c b/drivers/pinctrl/intel/pinctrl-intel.c
index 8085782cd8f9..9fc5bba514ea 100644
--- a/drivers/pinctrl/intel/pinctrl-intel.c
+++ b/drivers/pinctrl/intel/pinctrl-intel.c
@@ -1491,8 +1491,13 @@ 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;
-- 
2.30.1