platform/chrome: cros_kbd_led_backlight: allow binding through MFD

The ChromeOS EC used in Framework laptops supports the standard CrOS EC
keyboard backlight protocol.
However the firmware on these laptops doesn't implement the ACPI ID
GOOG0002 that is recognized by cros_kbd_led_backlight and they also
don't use device tree.

Prepare the existing cros_kbd_led_backlight driver to be probed through
the CrOS EC MFD device which works without ACPI or OF support.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20240526-cros_ec-kbd-led-framework-v3-3-ee577415a521@weissschuh.netSigned-off-by: Lee Jones <lee@kernel.org>

drivers/platform/chrome/Kconfig

@@ -150,7 +150,7 @@ config CROS_EC_PROTO
 
 config CROS_KBD_LED_BACKLIGHT
 	tristate "Backlight LED support for Chrome OS keyboards"
-	depends on LEDS_CLASS && (ACPI || CROS_EC)
+	depends on LEDS_CLASS && (ACPI || CROS_EC || MFD_CROS_EC_DEV)
 	help
 	  This option enables support for the keyboard backlight LEDs on
 	  select Chrome OS systems.

drivers/platform/chrome/cros_kbd_led_backlight.c

@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/leds.h>
+#include <linux/mfd/core.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -194,12 +195,45 @@ static const __maybe_unused struct keyboard_led_drvdata keyboard_led_drvdata_ec_
 
 #endif /* IS_ENABLED(CONFIG_CROS_EC) */
 
+#if IS_ENABLED(CONFIG_MFD_CROS_EC_DEV)
+static int keyboard_led_init_ec_pwm_mfd(struct platform_device *pdev)
+{
+	struct cros_ec_dev *ec_dev = dev_get_drvdata(pdev->dev.parent);
+	struct cros_ec_device *cros_ec = ec_dev->ec_dev;
+	struct keyboard_led *keyboard_led = platform_get_drvdata(pdev);
+
+	keyboard_led->ec = cros_ec;
+
+	return 0;
+}
+
+static const struct keyboard_led_drvdata keyboard_led_drvdata_ec_pwm_mfd = {
+	.init = keyboard_led_init_ec_pwm_mfd,
+	.brightness_set_blocking = keyboard_led_set_brightness_ec_pwm,
+	.brightness_get = keyboard_led_get_brightness_ec_pwm,
+	.max_brightness = KEYBOARD_BACKLIGHT_MAX,
+};
+
+#else /* IS_ENABLED(CONFIG_MFD_CROS_EC_DEV) */
+
+static const struct keyboard_led_drvdata keyboard_led_drvdata_ec_pwm_mfd = {};
+
+#endif /* IS_ENABLED(CONFIG_MFD_CROS_EC_DEV) */
+
+static int keyboard_led_is_mfd_device(struct platform_device *pdev)
+{
+	return IS_ENABLED(CONFIG_MFD_CROS_EC_DEV) && mfd_get_cell(pdev);
+}
+
 static int keyboard_led_probe(struct platform_device *pdev)
 {
 	const struct keyboard_led_drvdata *drvdata;
 	struct keyboard_led *keyboard_led;
 	int error;
 
+	if (keyboard_led_is_mfd_device(pdev))
+		drvdata = &keyboard_led_drvdata_ec_pwm_mfd;
+	else
 		drvdata = device_get_match_data(&pdev->dev);
 	if (!drvdata)
 		return -EINVAL;
@@ -216,13 +250,15 @@ static int keyboard_led_probe(struct platform_device *pdev)
 	}
 
 	keyboard_led->cdev.name = "chromeos::kbd_backlight";
-	keyboard_led->cdev.flags |= LED_CORE_SUSPENDRESUME;
+	keyboard_led->cdev.flags |= LED_CORE_SUSPENDRESUME | LED_REJECT_NAME_CONFLICT;
 	keyboard_led->cdev.max_brightness = drvdata->max_brightness;
 	keyboard_led->cdev.brightness_set = drvdata->brightness_set;
 	keyboard_led->cdev.brightness_set_blocking = drvdata->brightness_set_blocking;
 	keyboard_led->cdev.brightness_get = drvdata->brightness_get;
 
 	error = devm_led_classdev_register(&pdev->dev, &keyboard_led->cdev);
+	if (error == -EEXIST) /* Already bound via other mechanism */
+		return -ENODEV;
 	if (error)
 		return error;