[PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

["Pali Rohár" <pali.rohar@gmail.com>]

According to Dell WMI document mentioned in ML dicussion archived at
http://www.spinics.net/lists/platform-driver-x86/msg07220.html OS should
check Dell WMI descriptor structure. Structure also provide Dell WMI
interface version which is used later.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
---
 drivers/platform/x86/dell-wmi.c |   78 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
index 57402c4..09ee8ed 100644
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -2,6 +2,7 @@
  * Dell WMI hotkeys
  *
  * Copyright (C) 2008 Red Hat <mjg@redhat.com>
+ * Copyright (C) 2014-2015 Pali Rohár <pali.rohar@gmail.com>
  *
  * Portions based on wistron_btns.c:
  * Copyright (C) 2005 Miloslav Trmac <mitr@volny.cz>
@@ -38,14 +39,18 @@
 #include <acpi/video.h>
 
 MODULE_AUTHOR("Matthew Garrett <mjg@redhat.com>");
+MODULE_AUTHOR("Pali Rohár <pali.rohar@gmail.com>");
 MODULE_DESCRIPTION("Dell laptop WMI hotkeys driver");
 MODULE_LICENSE("GPL");
 
 #define DELL_EVENT_GUID "9DBB5994-A997-11DA-B012-B622A1EF5492"
+#define DELL_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-B622A1EF5492"
 
 static int acpi_video;
+static u32 dell_wmi_interface_version;
 
 MODULE_ALIAS("wmi:"DELL_EVENT_GUID);
+MODULE_ALIAS("wmi:"DELL_DESCRIPTOR_GUID);
 
 /*
  * Certain keys are flagged as KE_IGNORE. All of these are either
@@ -422,16 +427,85 @@ static void __init find_hk_type(const struct dmi_header *dm, void *dummy)
 	}
 }
 
+/**
+ * Descriptor buffer is 128 byte long and contains:
+ *
+ *       Name             Offset  Length  Value
+ * Vendor Signature          0       4    "DELL"
+ * Object Signature          4       4    " WMI"
+ * WMI Interface Version     8       4    <version>
+ * WMI buffer length        12       4    4096
+ */
+static int __init dell_wmi_check_descriptor_buffer(void)
+{
+	struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
+	union acpi_object *obj;
+	acpi_status status;
+	u32 *buffer;
+
+	status = wmi_query_block(DELL_DESCRIPTOR_GUID, 0, &out);
+	if (ACPI_FAILURE(status)) {
+		pr_err("Cannot read Dell descriptor buffer - %d\n", status);
+		return status;
+	}
+
+	obj = (union acpi_object *)out.pointer;
+	if (!obj) {
+		pr_err("Dell descriptor buffer is empty\n");
+		return -EINVAL;
+	}
+
+	if (obj->type != ACPI_TYPE_BUFFER) {
+		pr_err("Cannot read Dell descriptor buffer\n");
+		kfree(obj);
+		return -EINVAL;
+	}
+
+	if (obj->buffer.length != 128) {
+		pr_err("Dell descriptor buffer has invalid length (%d)\n",
+			obj->buffer.length);
+		kfree(obj);
+		return -EINVAL;
+	}
+
+	buffer = (u32 *)obj->buffer.pointer;
+
+	if (buffer[0] != 0x4C4C4544 && buffer[1] != 0x494D5720)
+		pr_warn("Dell descriptor buffer has invalid signature (%*ph)\n",
+			8, buffer);
+
+	if (buffer[2] != 0 && buffer[2] != 1)
+		pr_warn("Dell descriptor buffer has unknown version (%d)\n",
+			buffer[2]);
+
+	if (buffer[3] != 4096)
+		pr_warn("Dell descriptor buffer has invalid buffer length (%d)\n",
+			buffer[3]);
+
+	dell_wmi_interface_version = buffer[2];
+
+	pr_info("Detected Dell WMI interface version %u\n",
+		dell_wmi_interface_version);
+
+	kfree(obj);
+	return 0;
+}
+
 static int __init dell_wmi_init(void)
 {
 	int err;
 	acpi_status status;
 
-	if (!wmi_has_guid(DELL_EVENT_GUID)) {
-		pr_warn("No known WMI GUID found\n");
+	if (!wmi_has_guid(DELL_EVENT_GUID) ||
+	    !wmi_has_guid(DELL_DESCRIPTOR_GUID)) {
+		pr_warn("Dell WMI GUID were not found\n");
 		return -ENODEV;
 	}
 
+	err = dell_wmi_check_descriptor_buffer();
+	if (err)
+		return err;
+
 	dmi_walk(find_hk_type, NULL);
 	acpi_video = acpi_video_get_backlight_type() != acpi_backlight_vendor;
 
-- 
1.7.9.5