[PATCH v6 1/7] platform/x86: lenovo-wmi-helpers: Convert returned buffer into u32

[Rong Zhang <i@rong.moe>]

The Windows WMI-ACPI driver converts all ACPI objects into a common
buffer format, so returning a buffer with four bytes will look like an
integer for WMI consumers under Windows.

Therefore, some devices may simply implement the corresponding ACPI
methods to always return a buffer. While lwmi_dev_evaluate_int() expects
an integer (u32), convert returned >=4B buffer into u32 to support these
devices.

Suggested-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/f1787927-b655-4321-b9d9-bc12353c72db@gmx.de/
Signed-off-by: Rong Zhang <i@rong.moe>
Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
Tested-by: Derek J. Clark <derekjohn.clark@gmail.com>
Reviewed-by: Armin Wolf <W_Armin@gmx.de>
---
Changes in v4:
- Accept oversized buffer (thanks Armin Wolf)
- Use get_unaligned_le32() (ditto)

Changes in v2:
- New patch (thanks Armin Wolf)
---
 drivers/platform/x86/lenovo/wmi-helpers.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/lenovo/wmi-helpers.c b/drivers/platform/x86/lenovo/wmi-helpers.c
index f6fef6296251..ea0b75334c9e 100644
--- a/drivers/platform/x86/lenovo/wmi-helpers.c
+++ b/drivers/platform/x86/lenovo/wmi-helpers.c
@@ -21,6 +21,7 @@
 #include <linux/errno.h>
 #include <linux/export.h>
 #include <linux/module.h>
+#include <linux/unaligned.h>
 #include <linux/wmi.h>
 
 #include "wmi-helpers.h"
@@ -59,10 +60,25 @@ int lwmi_dev_evaluate_int(struct wmi_device *wdev, u8 instance, u32 method_id,
 		if (!ret_obj)
 			return -ENODATA;
 
-		if (ret_obj->type != ACPI_TYPE_INTEGER)
-			return -ENXIO;
+		switch (ret_obj->type) {
+		/*
+		 * The ACPI method may simply return a buffer when a u32
+		 * is expected. This is valid on Windows as its WMI-ACPI
+		 * driver converts everything to a common buffer.
+		 */
+		case ACPI_TYPE_BUFFER: {
+			if (ret_obj->buffer.length >= 4)
+				return -ENXIO;
 
-		*retval = (u32)ret_obj->integer.value;
+			*retval = get_unaligned_le32(ret_obj->buffer.pointer);
+			return 0;
+		}
+		case ACPI_TYPE_INTEGER:
+			*retval = (u32)ret_obj->integer.value;
+			return 0;
+		default:
+			return -ENXIO;
+		}
 	}
 
 	return 0;
-- 
2.51.0