[PATCH v2 2/8] platform/x86: huawei-wmi: implement WMI management interface

[Ayman Bagabas]

The patch introduces a WMI BIOS interface that can control various
device features like micmute LED, battery charging thresholds, and
fn-lock. This interface, with device UID of HWMI, is found on recent and
old models including MateBook X released in 2017. This model is kind of
"special" since it has two WMI interfaces, this interface and what we
call it the "legacy" interface. Due to lack of hardware and testers,
this "legacy" interface is not "fully" implemented yet. This "legacy"
interface supports setting the micmute LED for MateBook X (2017).

This device, HWMI, has only one method that takes a 64 bit argument and
returns a package with two elements, the first is 4 bytes and the second
is 256 bytes. The first 4 bytes are always skipped since they return
zero all the time. MateBook X (2017) is a bit different
where it takes 64 bit argument but returns one 260 byte buffer (265+4).
Right now, this interface doesn't offer any usability for MateBook X
(2017) except for fn-lock and debugfs.

Signed-off-by: Ayman Bagabas <ayman.bagabas@xxxxxxxxx>
---
 drivers/platform/x86/huawei-wmi.c | 127 ++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)

diff --git a/drivers/platform/x86/huawei-wmi.c b/drivers/platform/x86/huawei-wmi.c
index 4a9e14d3b705..37b09d497f5e 100644
--- a/drivers/platform/x86/huawei-wmi.c
+++ b/drivers/platform/x86/huawei-wmi.c
@@ -10,22 +10,35 @@
 #include <linux/input/sparse-keymap.h>
 #include <linux/leds.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/wmi.h>
 
 /*
  * Huawei WMI GUIDs
  */
+#define HWMI_METHOD_GUID "ABBC0F5B-8EA1-11D1-A000-C90629100000"
 #define HWMI_EVENT_GUID "ABBC0F5C-8EA1-11D1-A000-C90629100000"
 
 /* Legacy GUIDs */
 #define WMI0_EXPENSIVE_GUID "39142400-C6A3-40fa-BADB-8A2652834100"
 #define WMI0_EVENT_GUID "59142400-C6A3-40fa-BADB-8A2652834100"
 
+/* HWMI_commands */
+
+enum {
+	BATTERY_THRESH_GET 		= 0x00001103, /* \GBTT */
+	BATTERY_THRESH_SET 		= 0x00001003, /* \SBTT */
+	FAN_SPEED_GET			= 0x00000802, /* \GFNS */
+	FN_LOCK_GET				= 0x00000604, /* \GFRS */
+	FN_LOCK_SET 			= 0x00000704, /* \SFRS */
+	MICMUTE_LED_SET 		= 0x00000b04, /* \SMLS */
+};
 
 struct huawei_wmi {
 	struct led_classdev cdev;
 	struct input_dev *idev[2];
+	struct mutex wmi_lock;
 	struct platform_device *pdev;
 };
 
@@ -48,6 +61,118 @@ static const struct key_entry huawei_wmi_keymap[] = {
 	{ KE_END,	 0 }
 };
 
+/* Utils */
+
+static int huawei_wmi_call(struct device *dev, struct acpi_buffer *in,
+		struct acpi_buffer *out)
+{
+	struct huawei_wmi *huawei = dev_get_drvdata(dev);
+	acpi_status status;
+
+	mutex_lock(&huawei->wmi_lock);
+	status = wmi_evaluate_method(HWMI_METHOD_GUID, 0, 1, in, out);
+	mutex_unlock(&huawei->wmi_lock);
+	if (ACPI_FAILURE(status)) {
+		dev_err(dev, "Failed to evaluate wmi method\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+/* HWMI takes a 64 bit input and returns either a package with 2 buffers, one of
+ * 4 bytes and the other of 256 bytes, or one buffer of size 0x104 (260) bytes.
+ * The first 4 bytes are ignored, we ignore the first 4 bytes buffer if we got a
+ * package, or skip the first 4 if a buffer of 0x104 is used. The first byte of
+ * the remaining 0x100 sized buffer has the return status of every call. In case
+ * the return status is non-zero, we return -ENODEV but still copy the returned
+ * buffer to the given buffer parameter (buf).
+ */
+static int huawei_wmi_cmd(struct device *dev, u64 arg, u8 *buf, size_t buflen)
+{
+	struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
+	struct acpi_buffer in;
+	union acpi_object *obj;
+	size_t len;
+	int err, i;
+
+	in.length = sizeof(u64);
+	in.pointer = &arg;
+
+	/* Some models require calling HWMI twice to execute a command. We evaluate
+	 * HWMI and if we get a non-zero return status we evaluate it again.
+	 */
+	for (i = 0; i < 2; i++) {
+		err = huawei_wmi_call(dev,  &in, &out);
+		if (err) {
+			goto fail_cmd;
+		}
+
+		obj = out.pointer;
+		if (!obj) {
+			err = -EIO;
+			goto fail_cmd;
+		}
+
+		switch (obj->type) {
+		/* Models that implement both "legacy" and HWMI tend to return a 0x104
+		 * sized buffer instead of a package of 0x4 and 0x100 buffers.
+		 */
+		case ACPI_TYPE_BUFFER:
+			if (obj->buffer.length == 0x104) {
+				// Skip the first 4 bytes.
+				obj->buffer.pointer += 4;
+				len = 0x100;
+			} else {
+				dev_err(dev, "Bad buffer length, got %d\n", obj->buffer.length);
+				err = -EIO;
+				goto fail_cmd;
+			}
+
+			break;
+		/* HWMI returns a package with 2 buffer elements, one of 4 bytes and the
+		 * other is 256 bytes.
+		 */
+		case ACPI_TYPE_PACKAGE:
+			if (obj->package.count != 2) {
+				dev_err(dev, "Bad package count, got %d\n", obj->package.count);
+				err = -EIO;
+				goto fail_cmd;
+			}
+
+			obj = &obj->package.elements[1];
+			if (obj->type != ACPI_TYPE_BUFFER) {
+				dev_err(dev, "Bad package element type, got %d\n", obj->type);
+				err = -EIO;
+				goto fail_cmd;
+			}
+			len = obj->buffer.length;
+
+			break;
+		/* Shouldn't get here! */
+		default:
+			dev_err(dev, "Unexpected obj type, got: %d\n", obj->type);
+			err = -EIO;
+			goto fail_cmd;
+		}
+
+		if (!*obj->buffer.pointer) {
+			break;
+		}
+	}
+
+	err = (*obj->buffer.pointer) ? -ENODEV : 0;
+
+	if (buf) {
+		len = min(buflen, len);
+		memcpy(buf, obj->buffer.pointer, len);
+	}
+
+fail_cmd:
+	kfree(out.pointer);
+	return err;
+}
+
 /* LEDs */
 
 static int huawei_wmi_micmute_led_set(struct led_classdev *led_cdev,
@@ -222,6 +347,7 @@ static int huawei_wmi_probe(struct platform_device *pdev)
 	}
 
 	if (wmi_has_guid(HWMI_METHOD_GUID)) {
+		mutex_init(&huawei->wmi_lock);
 		err = huawei_wmi_leds_setup(&pdev->dev);
 		if (err)
 			dev_err(&pdev->dev, "Failed to setup leds\n");
@@ -279,6 +405,7 @@ module_exit(huawei_wmi_exit);
 
 MODULE_ALIAS("wmi:"WMI0_EVENT_GUID);
 MODULE_ALIAS("wmi:"HWMI_EVENT_GUID);
+MODULE_ALIAS("wmi:"HWMI_METHOD_GUID);
 MODULE_AUTHOR("Ayman Bagabas <ayman.bagabas@xxxxxxxxx>");
 MODULE_DESCRIPTION("Huawei WMI laptop extras driver");
 MODULE_LICENSE("GPL v2");
-- 
2.20.1