[PATCH] serdev: Fix detection of UART devices on Apple machines.

["Ronald Tschalär" <ronald@innovation.ch>]

On Apple devices the _CRS method returns an empty resource template, and
the resource settings are instead provided by the _DSM method. But
commit 33364d63c75d6182fa369cea80315cf1bb0ee38e (serdev: Add ACPI
devices by ResourceSource field) changed the search for serdev devices
to require valid, non-empty resource template, thereby breaking Apple
devices and causing bluetooth devices to not be found.

This expands the check so that if we don't find a valid template, and
we're on an Apple machine, then just check for the device being an
immediate child of the controller and having a "baud" property.

Cc: <stable@vger.kernel.org> # 5.5
Signed-off-by: Ronald Tschalär <ronald@innovation.ch>
---
 drivers/tty/serdev/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
index ce5309d00280..0f64a10ba51f 100644
--- a/drivers/tty/serdev/core.c
+++ b/drivers/tty/serdev/core.c
@@ -18,6 +18,7 @@
 #include <linux/sched.h>
 #include <linux/serdev.h>
 #include <linux/slab.h>
+#include <linux/platform_data/x86/apple.h>
 
 static bool is_registered;
 static DEFINE_IDA(ctrl_ida);
@@ -630,6 +631,15 @@ static int acpi_serdev_check_resources(struct serdev_controller *ctrl,
 	if (ret)
 		return ret;
 
+	/*
+	 * Apple machines provide an empty resource template, so on those
+	 * machines just look for immediate children with a "baud" property
+	 * (from the _DSM method) instead.
+	 */
+	if (!lookup.controller_handle && x86_apple_machine &&
+	    !acpi_dev_get_property(adev, "baud", ACPI_TYPE_BUFFER, NULL))
+		acpi_get_parent(adev->handle, &lookup.controller_handle);
+
 	/* Make sure controller and ResourceSource handle match */
 	if (ACPI_HANDLE(ctrl->dev.parent) != lookup.controller_handle)
 		return -ENODEV;
-- 
2.24.1