Input: soc_button_array - partial revert of support for newer surface devices

Commit c394159310 ("Input: soc_button_array - add support for newer
surface devices") not only added support for the MSHW0040 ACPI HID,
but for some reason it also makes changes to the error handling of the
soc_button_lookup_gpio() call in soc_button_device_create(). Note ideally
this seamingly unrelated change would have been made in a separate commit,
with a message explaining the what and why of this change.

I guess this change may have been added to deal with -EPROBE_DEFER errors,
but in case of the existing support for PNP0C40 devices, treating
-EPROBE_DEFER as any other error is deliberate, see the comment this
commit adds for why.

The actual returning of -EPROBE_DEFER to the caller of soc_button_probe()
introduced by the new error checking causes a serious regression:

On devices with so called virtual GPIOs soc_button_lookup_gpio() will
always return -EPROBE_DEFER for these fake GPIOs, when this happens
during the second call of soc_button_device_create() we already have
successfully registered our first child. This causes the kernel to think
we are making progress with probing things even though we unregister the
child before again before we return the -EPROBE_DEFER. Since we are making
progress the kernel will retry deferred-probes again immediately ending
up stuck in a loop with the following showing in dmesg:

[  124.022697] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6537
[  124.040764] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6538
[  124.056967] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6539
[  124.072143] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6540
[  124.092373] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6541
[  124.108065] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6542
[  124.128483] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6543
[  124.147141] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6544
[  124.165070] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6545
[  124.179775] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6546
[  124.202726] input: gpio-keys as /devices/platform/INTCFD9:00/gpio-keys.0.auto/input/input6547
<continues on and on and on>

And 1 CPU core being stuck at 100% and udev hanging since it is waiting
for the modprobe of soc_button_array to return.

This patch reverts the soc_button_lookup_gpio() error handling changes,
fixing this regression.

Fixes: c394159310 ("Input: soc_button_array - add support for newer surface devices")
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=205031
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Maximilian Luz <luzmaximilian@gmail.com>
Acked-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20191005105551.353273-1-hdegoede@redhat.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/soc_button_array.c

@@ -92,11 +92,18 @@ soc_button_device_create(struct platform_device *pdev,
 			continue;
 
 		gpio = soc_button_lookup_gpio(&pdev->dev, info->acpi_index);
-		if (gpio < 0 && gpio != -ENOENT) {
-			error = gpio;
-			goto err_free_mem;
-		} else if (!gpio_is_valid(gpio)) {
-			/* Skip GPIO if not present */
+		if (!gpio_is_valid(gpio)) {
+			/*
+			 * Skip GPIO if not present. Note we deliberately
+			 * ignore -EPROBE_DEFER errors here. On some devices
+			 * Intel is using so called virtual GPIOs which are not
+			 * GPIOs at all but some way for AML code to check some
+			 * random status bits without need a custom opregion.
+			 * In some cases the resources table we parse points to
+			 * such a virtual GPIO, since these are not real GPIOs
+			 * we do not have a driver for these so they will never
+			 * show up, therefore we ignore -EPROBE_DEFER.
+			 */
 			continue;
 		}