Add support for WMMX method

This should support at least the Lenovo Ideapad Y470 and Y570. It probes the
WMMX method before calling the _DSM method directly since that method should
work for all machines that support the NVIDIA DSM.

bbswitch.c

@@ -41,6 +41,8 @@ static const char acpi_optimus_dsm_muid[16] = {
     0xA7, 0x2B, 0x60, 0x42, 0xA6, 0xB5, 0xBE, 0xE0,
 };
 
+#define MXM_WMMX_GUID "F6CB5C3C-9CAE-4EBD-B577-931EA32A2CC0"
+#define MXM_WMMX_FUNC_DSM 0x4D53445F /* NVIDIA DSM */
 static const char acpi_nvidia_dsm_muid[16] = {
     0xA0, 0xA0, 0x95, 0x9D, 0x60, 0x00, 0x48, 0x4D,
     0xB3, 0x4D, 0x7E, 0x5F, 0xEA, 0x12, 0x9F, 0xD4
@@ -56,10 +58,22 @@ It looks like something for Intel GPU:
 http://lxr.linux.no/#linux+v3.1.5/drivers/gpu/drm/i915/intel_acpi.c
  */
 
-#define DSM_TYPE_UNSUPPORTED    0
+struct mxdsm_args {
-#define DSM_TYPE_OPTIMUS        1
+    u32 func;
-#define DSM_TYPE_NVIDIA         2
+    char muid[16];
-static int dsm_type = DSM_TYPE_UNSUPPORTED;
+    u32 revid;
+    u32 sfnc;
+    char args[4];
+};
+
+enum dsm_type {
+    DSM_TYPE_UNSUPPORTED,
+    DSM_TYPE_OPTIMUS,
+    DSM_TYPE_NVIDIA,
+    /* _DSM call through a WMI MX method */
+    DSM_TYPE_NVIDIA_WMI,
+};
+static enum dsm_type dsm_type = DSM_TYPE_UNSUPPORTED;
 
 static struct pci_dev *dis_dev;
 static acpi_handle dis_handle;
@@ -78,6 +92,8 @@ static char *buffer_to_string(const char buffer[], char *target) {
     return target;
 }
 
+static int parse_dsm_result(struct acpi_buffer *output, uint32_t *result);
+
 // Returns 0 if the call succeeded and non-zero otherwise. If the call
 // succeeded, the result is stored in "result" providing that the result is an
 // integer or a buffer containing 4 values
@@ -86,7 +102,6 @@ static int acpi_call_dsm(acpi_handle handle, const char muid[16], int revid,
     struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
     struct acpi_object_list input;
     union acpi_object params[4];
-    union acpi_object *obj;
     int err;
 
     input.count = 4;
@@ -118,8 +133,12 @@ static int acpi_call_dsm(acpi_handle handle, const char muid[16], int revid,
             buffer_to_string(args, tmp), acpi_format_exception(err));
         return err;
     }
+    return parse_dsm_result(&output, result);
+}
 
-    obj = (union acpi_object *)output.pointer;
+// Processes the result of an ACPI _DSM call and deallocates the result memory
+static int parse_dsm_result(struct acpi_buffer *output, uint32_t *result) {
+    union acpi_object *obj = output->pointer;
 
     if (obj->type == ACPI_TYPE_INTEGER && result) {
         *result = obj->integer.value;
@@ -136,7 +155,7 @@ static int acpi_call_dsm(acpi_handle handle, const char muid[16], int revid,
             " type: %X\n", obj->type);
     }
 
-    kfree(output.pointer);
+    kfree(output->pointer);
     return 0;
 }
 
@@ -153,6 +172,51 @@ static int has_dsm_func(const char muid[16], int revid, int sfnc) {
     return result & 1 && result & (1 << sfnc);
 }
 
+// Returns 0 if the call succeeded and non-zero otherwise. If the call
+// succeeded, the result is stored in "result" providing that the result is an
+// integer or a buffer containing 4 values
+static int wmmx_call(const char muid[16], int revid, int func, char args[4],
+    uint32_t *result) {
+    struct mxdsm_args mx_args = {
+        .func = MXM_WMMX_FUNC_DSM,
+        .revid = revid,
+        .sfnc = func,
+    };
+    struct acpi_buffer input = { (acpi_size)sizeof(mx_args), &mx_args };
+    struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
+    acpi_status status;
+
+    memcpy(mx_args.muid, muid, sizeof(mx_args.muid));
+    if (args) {
+        memcpy(mx_args.args, args, sizeof(mx_args.args));
+    } else {
+        // some implementations do not like empty values
+        memset(mx_args.args, 0, sizeof(mx_args.args));
+    }
+
+    // 1, > 1 <-- required by at least Acer Travelmate 8472TG, seen on others
+    status = wmi_evaluate_method(MXM_WMMX_GUID, 1, 1, &input, &output);
+    if (ACPI_FAILURE(status)) {
+        printk(KERN_WARNING "bbswitch: failed to evaluate WMMX: %s\n",
+            acpi_format_exception(status));
+        return status;
+    }
+    return parse_dsm_result(&output, result);
+}
+
+// Returns 1 if a _DSM function and its function index exists and 0 otherwise
+static int has_wmi_func(const char muid[16], int revid, int sfnc) {
+    u32 result = 0;
+
+    // fail if the _DSM call failed
+    if (wmmx_call(muid, revid, 0, 0, &result))
+        return 0;
+
+    // ACPI Spec v4 9.14.1: if bit 0 is zero, no function is supported. If
+    // the n-th bit is enabled, function n is supported
+    return result & 1 && result & (1 << sfnc);
+}
+
 static int bbswitch_optimus_dsm(void) {
     if (dsm_type == DSM_TYPE_OPTIMUS) {
         char args[] = {1, 0, 0, 3};
@@ -170,10 +234,9 @@ static int bbswitch_optimus_dsm(void) {
 }
 
 static int bbswitch_acpi_off(void) {
+    char args[] = {2, 0, 0, 0};
+    u32 result = 0;
     if (dsm_type == DSM_TYPE_NVIDIA) {
-        char args[] = {2, 0, 0, 0};
-        u32 result = 0;
-
         if (acpi_call_dsm(dis_handle, acpi_nvidia_dsm_muid, 0x102, 0x3, args,
             &result)) {
             // failure
@@ -181,15 +244,21 @@ static int bbswitch_acpi_off(void) {
         }
         printk(KERN_DEBUG "bbswitch: Result of _DSM call for OFF: %08X\n",
             result);
+    } else if (dsm_type == DSM_TYPE_NVIDIA_WMI) {
+        if (wmmx_call(acpi_nvidia_dsm_muid, 0x102, 0x3, args, &result)) {
+            // failure
+            return 1;
+        }
+        printk(KERN_DEBUG "bbswitch: Result of WMMX call for OFF: %08X\n",
+            result);
     }
     return 0;
 }
 
 static int bbswitch_acpi_on(void) {
+    char args[] = {1, 0, 0, 0};
+    u32 result = 0;
     if (dsm_type == DSM_TYPE_NVIDIA) {
-        char args[] = {1, 0, 0, 0};
-        u32 result = 0;
-
         if (acpi_call_dsm(dis_handle, acpi_nvidia_dsm_muid, 0x102, 0x3, args,
             &result)) {
             // failure
@@ -197,6 +266,13 @@ static int bbswitch_acpi_on(void) {
         }
         printk(KERN_DEBUG "bbswitch: Result of _DSM call for ON: %08X\n",
             result);
+    } else if (dsm_type == DSM_TYPE_NVIDIA_WMI) {
+        if (wmmx_call(acpi_nvidia_dsm_muid, 0x102, 0x3, args, &result)) {
+            // failure
+            return 1;
+        }
+        printk(KERN_DEBUG "bbswitch: Result of WMMX call for ON: %08X\n",
+            result);
     }
     return 0;
 }
@@ -369,6 +445,9 @@ static int __init bbswitch_init(void) {
     if (has_dsm_func(acpi_optimus_dsm_muid, 0x100, 0x1A)) {
         dsm_type = DSM_TYPE_OPTIMUS;
         printk(KERN_INFO "bbswitch: detected an Optimus _DSM function\n");
+    } else if (has_wmi_func(acpi_nvidia_dsm_muid, 0x102, 0x3)) {
+        dsm_type = DSM_TYPE_NVIDIA_WMI;
+        printk(KERN_INFO "bbswitch: detected a nVidia WMMX function\n");
     } else if (has_dsm_func(acpi_nvidia_dsm_muid, 0x102, 0x3)) {
         dsm_type = DSM_TYPE_NVIDIA;
         printk(KERN_INFO "bbswitch: detected a nVidia _DSM function\n");