[PATCH v3] platform/x86: Add driver for ACPI WMAA EC-based backlight control

[Daniel Dadap <ddadap@nvidia.com>]

A number of upcoming notebook computer designs drive the internal
display panel's backlight PWM through the Embedded Controller (EC).
This EC-based backlight control can be plumbed through to an ACPI
"WMAA" method interface, which in turn can be wrapped by WMI with
the GUID handle 603E9613-EF25-4338-A3D0-C46177516DB7.

Add a new driver, aliased to the WMAA WMI GUID, to expose a sysfs
backlight class driver to control backlight levels on systems with
EC-driven backlights.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Daniel Dadap <ddadap@nvidia.com>
---

v2: Convert to WMI subsystem driver, suggested by Mario Limonciello
    <mario.limonciello@outlook.com>; various cleanups suggested by
    Barnabás Pőcze <pobrn@protonmail.com>
v3: Address assorted style nits raised by Andy Shevchenko
    <andy.shevchenko@gmail.com> in response to a related patch; remove
    additional behavior change to WMI subsystem from patch series as
    recommended by Hans de Goede <hdegoede@redhat.com>

 MAINTAINERS                               |   6 +
 drivers/platform/x86/Kconfig              |  10 ++
 drivers/platform/x86/Makefile             |   1 +
 drivers/platform/x86/wmaa-backlight-wmi.c | 184 ++++++++++++++++++++++
 4 files changed, 201 insertions(+)
 create mode 100644 drivers/platform/x86/wmaa-backlight-wmi.c

diff --git a/MAINTAINERS b/MAINTAINERS
index bbaecde94aa0..fd7362a86c6d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20008,6 +20008,12 @@ L:	linux-wireless@vger.kernel.org
 S:	Odd fixes
 F:	drivers/net/wireless/wl3501*
 
+WMAA BACKLIGHT DRIVER
+M:	Daniel Dadap <ddadap@nvidia.com>
+L:	platform-driver-x86@vger.kernel.org
+S:	Supported
+F:	drivers/platform/x86/wmaa-backlight-wmi.c
+
 WOLFSON MICROELECTRONICS DRIVERS
 L:	patches@opensource.cirrus.com
 S:	Supported
diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index d12db6c316ea..e54449c16d03 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -113,6 +113,16 @@ config PEAQ_WMI
 	help
 	 Say Y here if you want to support WMI-based hotkeys on PEAQ 2-in-1s.
 
+config WMAA_BACKLIGHT_WMI
+	tristate "ACPI WMAA Backlight Driver"
+	depends on ACPI_WMI
+	depends on BACKLIGHT_CLASS_DEVICE
+	help
+	  This driver provides a sysfs backlight interface for notebook
+	  systems which expose the WMAA ACPI method and an associated WMI
+	  wrapper to drive LCD backlight levels through the system's
+	  Embedded Controller.
+
 config XIAOMI_WMI
 	tristate "Xiaomi WMI key driver"
 	depends on ACPI_WMI
diff --git a/drivers/platform/x86/Makefile b/drivers/platform/x86/Makefile
index 7ee369aab10d..109c1714237d 100644
--- a/drivers/platform/x86/Makefile
+++ b/drivers/platform/x86/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_INTEL_WMI_SBL_FW_UPDATE)	+= intel-wmi-sbl-fw-update.o
 obj-$(CONFIG_INTEL_WMI_THUNDERBOLT)	+= intel-wmi-thunderbolt.o
 obj-$(CONFIG_MXM_WMI)			+= mxm-wmi.o
 obj-$(CONFIG_PEAQ_WMI)			+= peaq-wmi.o
+obj-$(CONFIG_WMAA_BACKLIGHT_WMI)	+= wmaa-backlight-wmi.o
 obj-$(CONFIG_XIAOMI_WMI)		+= xiaomi-wmi.o
 obj-$(CONFIG_GIGABYTE_WMI)		+= gigabyte-wmi.o
 
diff --git a/drivers/platform/x86/wmaa-backlight-wmi.c b/drivers/platform/x86/wmaa-backlight-wmi.c
new file mode 100644
index 000000000000..b607d3f88fc2
--- /dev/null
+++ b/drivers/platform/x86/wmaa-backlight-wmi.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/acpi.h>
+#include <linux/backlight.h>
+#include <linux/module.h>
+#include <linux/wmi.h>
+
+#define WMAA_WMI_GUID "603E9613-EF25-4338-A3D0-C46177516DB7"
+
+struct wmi_wmaa_priv {
+	struct backlight_device *backlight;
+};
+
+enum wmaa_method {
+	WMAA_BRIGHTNESS_LEVEL = 1,
+	WMAA_BRIGHTNESS_SOURCE = 2,
+};
+
+enum wmaa_get_or_set {
+	WMAA_GET = 0,
+	WMAA_SET = 1,
+	WMAA_GET_MAX = 2, // for WMAA_BRIGHTNESS_LEVEL only
+};
+
+enum wmaa_source {
+	WMAA_SOURCE_CLEAR = 0,
+	WMAA_SOURCE_GPU = 1,
+	WMAA_SOURCE_EC = 2,
+	WMAA_SOURCE_AUX = 3,
+	WMAA_SOURCE_COUNT
+};
+
+struct wmaa_args {
+	u32 set;
+	u32 val;
+	u32 ret;
+	u32 ignored[3];
+};
+
+static const struct wmi_device_id wmaa_backlight_wmi_id_table[] = {
+	{ .guid_string = WMAA_WMI_GUID },
+	{ },
+};
+
+static struct wmi_device *wdev;
+
+static int wmi_call_wmaa(enum wmaa_method method, enum wmaa_get_or_set set, u32 *val)
+{
+	struct wmaa_args args = {
+		.set = set,
+		.val = 0,
+		.ret = 0,
+	};
+	struct acpi_buffer buf = { (acpi_size)sizeof(args), &args };
+	acpi_status status;
+
+	if (set == WMAA_SET)
+		args.val = *val;
+
+	status = wmidev_evaluate_method(wdev, 0, method, &buf, &buf);
+	if (ACPI_FAILURE(status)) {
+		pr_err("ACPI WMAA failed with %s\n", acpi_format_exception(status));
+		return -EIO;
+	}
+
+	if (set != WMAA_SET)
+		*val = args.ret;
+
+	return 0;
+}
+
+static int wmaa_get_brightness(u32 *level)
+{
+	return wmi_call_wmaa(WMAA_BRIGHTNESS_LEVEL, WMAA_GET, level);
+}
+
+static int wmaa_set_brightness(u32 level)
+{
+	return wmi_call_wmaa(WMAA_BRIGHTNESS_LEVEL, WMAA_SET, &level);
+}
+
+static int wmaa_backlight_update_status(struct backlight_device *bd)
+{
+	return wmaa_set_brightness(bd->props.brightness);
+}
+
+static int wmaa_backlight_get_brightness(struct backlight_device *bd)
+{
+	u32 level;
+	int ret;
+
+	ret = wmaa_get_brightness(&level);
+
+	WARN_ON(ret != 0);
+	return ret == 0 ? level : 0;
+}
+
+static const struct backlight_ops wmaa_backlight_ops = {
+	.update_status = wmaa_backlight_update_status,
+	.get_brightness = wmaa_backlight_get_brightness,
+};
+
+static int wmaa_get_max_brightness(u32 *level)
+{
+	return wmi_call_wmaa(WMAA_BRIGHTNESS_LEVEL, WMAA_GET_MAX, level);
+}
+
+static int wmaa_get_brightness_source(u32 *source)
+{
+	return wmi_call_wmaa(WMAA_BRIGHTNESS_SOURCE, WMAA_GET, source);
+}
+
+static int wmaa_backlight_wmi_probe(struct wmi_device *w, const void *ctx)
+{
+	struct backlight_properties props = {0};
+	struct wmi_wmaa_priv *priv;
+	u32 source;
+	int ret;
+
+	priv = devm_kmalloc(&w->dev, sizeof(*priv), GFP_KERNEL);
+	if(!priv)
+		return -ENOMEM;
+
+	wdev = w;
+
+	ret = wmaa_get_brightness_source(&source);
+	if (ret)
+		goto done;
+
+	if (source != WMAA_SOURCE_EC) {
+		ret = -ENODEV;
+		goto done;
+	}
+
+	// Register a backlight handler
+	props.type = BACKLIGHT_PLATFORM;
+	ret = wmaa_get_max_brightness(&props.max_brightness);
+	if (ret)
+		goto done;
+
+	ret = wmaa_get_brightness(&props.brightness);
+	if (ret)
+		goto done;
+
+	priv->backlight = backlight_device_register("wmaa_backlight",
+		NULL, NULL, &wmaa_backlight_ops, &props);
+	if (IS_ERR(priv->backlight))
+		return PTR_ERR(priv->backlight);
+
+	dev_set_drvdata(&w->dev, priv);
+
+done:
+	return ret;
+}
+
+static void wmaa_backlight_wmi_remove(struct wmi_device *wdev)
+{
+	struct wmi_wmaa_priv *priv = dev_get_drvdata(&wdev->dev);
+
+	backlight_device_unregister(priv->backlight);
+}
+
+static struct wmi_driver wmaa_backlight_wmi_driver = {
+	.driver = {
+		.name = "wmaa-backlight",
+	},
+	.probe = wmaa_backlight_wmi_probe,
+	.remove = wmaa_backlight_wmi_remove,
+	.id_table = wmaa_backlight_wmi_id_table,
+};
+
+module_wmi_driver(wmaa_backlight_wmi_driver);
+
+MODULE_AUTHOR("Aaron Plattner <aplattner@nvidia.com>");
+MODULE_AUTHOR("Daniel Dadap <ddadap@nvidia.com>");
+MODULE_DESCRIPTION("WMAA Backlight WMI driver");
+MODULE_LICENSE("GPL v2");
+
+MODULE_ALIAS("wmi:"WMAA_WMI_GUID);
-- 
2.20.1