Re: [PATCH v3 2/2] platform/chrome: Add Wilco EC keyboard backlight LEDs support

[Enric Balletbo i Serra <enric.balletbo@collabora.com>]

Hi Nick,

On 3/4/19 4:05, Nick Crews wrote:
> The EC is in charge of controlling the keyboard backlight on
> the Wilco platform. We expose a standard LED class device at
> /sys/class/leds/chromeos::kbd_backlight. This driver is modeled
> after the standard Chrome OS keyboard backlight driver at
> drivers/platform/chrome/cros_kbd_led_backlight.c
> 
> Some Wilco devices do not support a keyboard backlight. This
> is checked via wilco_ec_keyboard_leds_exist() in the core driver,
> and a platform_device will only be registered by the core if
> a backlight is supported.
> 
> After an EC reset the backlight could be in a non-PWM mode.
> Earlier in the boot sequence the BIOS should send a command to
> the EC to set the brightness, so things **should** be set up,
> but we double check in probe() as we query the initial brightness.
> If not set up, then set the brightness to 0.
> 
> Since the EC will never change the backlight level of its own accord,
> we don't need to implement a brightness_get() method.
> 
> v3 changes:
> -Since this behaves the same as the standard Chrome OS keyboard
>  backlight, rename the led device to "chromeos::kbd_backlight"
> -Move wilco_ec_keyboard_backlight_exists() into core module, so
>  that the core does not depend upon the keyboard backlight driver.
> -This required moving some code into wilco-ec.h
> -Refactor out some common code in set_brightness() and
>  initialize_brightness()
> 
> v2 changes:
> -Remove and fix uses of led vs LED in kconfig
> -Assume BIOS initializes brightness, but double check in probe()
> -Remove get_brightness() callback, as EC never changes brightness
>  by itself.
> -Use a __packed struct as message instead of opaque array
> -Add exported wilco_ec_keyboard_leds_exist() so the core driver
>  now only creates a platform _device if relevant
> -Fix use of keyboard_led_set_brightness() since it can sleep
> 
> Signed-off-by: Nick Crews <ncrews@chromium.org>
> ---
>  drivers/platform/chrome/wilco_ec/Kconfig      |   9 +
>  drivers/platform/chrome/wilco_ec/Makefile     |   2 +
>  drivers/platform/chrome/wilco_ec/core.c       |  58 ++++++
>  .../chrome/wilco_ec/kbd_led_backlight.c       | 167 ++++++++++++++++++

I'm fine with this patch, I'll wait to see if any of the LEDS subsystem
maintainer can give you an ack or review.

Thanks,
 Enric


>  include/linux/platform_data/wilco-ec.h        |  38 ++++
>  5 files changed, 274 insertions(+)
>  create mode 100644 drivers/platform/chrome/wilco_ec/kbd_led_backlight.c
> 
> diff --git a/drivers/platform/chrome/wilco_ec/Kconfig b/drivers/platform/chrome/wilco_ec/Kconfig
> index e09e4cebe9b4..d8cf4a60d1b5 100644
> --- a/drivers/platform/chrome/wilco_ec/Kconfig
> +++ b/drivers/platform/chrome/wilco_ec/Kconfig
> @@ -18,3 +18,12 @@ config WILCO_EC_DEBUGFS
>  	  manipulation and allow for testing arbitrary commands.  This
>  	  interface is intended for debug only and will not be present
>  	  on production devices.
> +
> +config WILCO_EC_KBD_BACKLIGHT
> +	tristate "Enable keyboard backlight control"
> +	depends on WILCO_EC
> +	help
> +	  If you say Y here, you get support to set the keyboard backlight
> +	  brightness. This happens via a standard LED driver that uses the
> +	  Wilco EC mailbox interface. A standard LED class device will
> +	  appear under /sys/class/leds/chromeos::kbd_backlight
> diff --git a/drivers/platform/chrome/wilco_ec/Makefile b/drivers/platform/chrome/wilco_ec/Makefile
> index 063e7fb4ea17..8436539813cd 100644
> --- a/drivers/platform/chrome/wilco_ec/Makefile
> +++ b/drivers/platform/chrome/wilco_ec/Makefile
> @@ -4,3 +4,5 @@ wilco_ec-objs				:= core.o mailbox.o
>  obj-$(CONFIG_WILCO_EC)			+= wilco_ec.o
>  wilco_ec_debugfs-objs			:= debugfs.o
>  obj-$(CONFIG_WILCO_EC_DEBUGFS)		+= wilco_ec_debugfs.o
> +wilco_kbd_backlight-objs		:= kbd_led_backlight.o
> +obj-$(CONFIG_WILCO_EC_KBD_BACKLIGHT)	+= wilco_kbd_backlight.o
> diff --git a/drivers/platform/chrome/wilco_ec/core.c b/drivers/platform/chrome/wilco_ec/core.c
> index 05e1e2be1c91..3c45c157b7da 100644
> --- a/drivers/platform/chrome/wilco_ec/core.c
> +++ b/drivers/platform/chrome/wilco_ec/core.c
> @@ -38,11 +38,47 @@ static struct resource *wilco_get_resource(struct platform_device *pdev,
>  				   dev_name(dev));
>  }
>  
> +/**
> + * wilco_ec_keyboard_backlight_exists() - Is the keyboad backlight supported?

Typo s/keyboad/keyboard/ don't need to resend for this.

> + * @ec: EC device to query.
> + * @exists: Return value to fill in.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +static int wilco_ec_keyboard_backlight_exists(struct wilco_ec_device *ec,
> +					      bool *exists)
> +{
> +	struct wilco_ec_kbbl_msg request;
> +	struct wilco_ec_kbbl_msg response;
> +	struct wilco_ec_message msg;
> +	int ret;
> +
> +	memset(&request, 0, sizeof(request));
> +	request.command = WILCO_EC_COMMAND_KBBL;
> +	request.subcmd = WILCO_KBBL_SUBCMD_GET_FEATURES;
> +
> +	memset(&msg, 0, sizeof(msg));
> +	msg.type = WILCO_EC_MSG_LEGACY;
> +	msg.request_data = &request;
> +	msg.request_size = sizeof(request);
> +	msg.response_data = &response;
> +	msg.response_size = sizeof(response);
> +
> +	ret = wilco_ec_mailbox(ec, &msg);
> +	if (ret < 0)
> +		return ret;
> +
> +	*exists = response.status != 0xFF;
> +
> +	return 0;
> +}
> +
>  static int wilco_ec_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
>  	struct wilco_ec_device *ec;
>  	int ret;
> +	bool kbbl_exists;
>  
>  	ec = devm_kzalloc(dev, sizeof(*ec), GFP_KERNEL);
>  	if (!ec)
> @@ -89,8 +125,29 @@ static int wilco_ec_probe(struct platform_device *pdev)
>  		goto unregister_debugfs;
>  	}
>  
> +	/* Register child dev to be found by the keyboard backlight driver. */
> +	ret = wilco_ec_keyboard_backlight_exists(ec, &kbbl_exists);
> +	if (ret) {
> +		dev_err(ec->dev,
> +			"Failed checking keyboard backlight support: %d", ret);
> +		goto unregister_rtc;
> +	}
> +	if (kbbl_exists) {
> +		ec->kbbl_pdev = platform_device_register_data(dev,
> +						"wilco-kbd-backlight",
> +						PLATFORM_DEVID_AUTO, NULL, 0);
> +		if (IS_ERR(ec->kbbl_pdev)) {
> +			dev_err(dev,
> +				"Failed to create keyboard backlight pdev\n");
> +			ret = PTR_ERR(ec->kbbl_pdev);
> +			goto unregister_rtc;
> +		}
> +	}
> +
>  	return 0;
>  
> +unregister_rtc:
> +	platform_device_unregister(ec->rtc_pdev);
>  unregister_debugfs:
>  	if (ec->debugfs_pdev)
>  		platform_device_unregister(ec->debugfs_pdev);
> @@ -102,6 +159,7 @@ static int wilco_ec_remove(struct platform_device *pdev)
>  {
>  	struct wilco_ec_device *ec = platform_get_drvdata(pdev);
>  
> +	platform_device_unregister(ec->kbbl_pdev);
>  	platform_device_unregister(ec->rtc_pdev);
>  	if (ec->debugfs_pdev)
>  		platform_device_unregister(ec->debugfs_pdev);
> diff --git a/drivers/platform/chrome/wilco_ec/kbd_led_backlight.c b/drivers/platform/chrome/wilco_ec/kbd_led_backlight.c
> new file mode 100644
> index 000000000000..922ac8717b23
> --- /dev/null
> +++ b/drivers/platform/chrome/wilco_ec/kbd_led_backlight.c
> @@ -0,0 +1,167 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Keyboard backlight LED driver for the Wilco Embedded Controller
> + *
> + * Copyright 2019 Google LLC
> + *
> + * The EC is in charge of controlling the keyboard backlight on
> + * the Wilco platform. We expose a standard LED class device at
> + * /sys/class/leds/chromeos::kbd_backlight. Power Manager normally
> + * controls the backlight by writing a percentage in range [0, 100]
> + * to the brightness property. This driver is modeled after the
> + * standard Chrome OS keyboard backlight driver at
> + * drivers/platform/chrome/cros_kbd_led_backlight.c
> + *
> + * Some Wilco devices do not support a keyboard backlight. This
> + * is checked via wilco_ec_keyboard_backlight_exists() in the core driver,
> + * and a platform_device will only be registered by the core if
> + * a backlight is supported.
> + *
> + * After an EC reset the backlight could be in a non-PWM mode.
> + * Earlier in the boot sequence the BIOS should send a command to
> + * the EC to set the brightness, so things **should** be set up,
> + * but we double check in probe() as we query the initial brightness.
> + * If not set up, then we set the brightness to KBBL_DEFAULT_BRIGHTNESS.
> + *
> + * Since the EC will never change the backlight level of its own accord,
> + * we don't need to implement a brightness_get() method.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/leds.h>
> +#include <linux/module.h>
> +#include <linux/platform_data/wilco-ec.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +#define DRV_NAME		"wilco-kbd-backlight"
> +
> +#define KBBL_DEFAULT_BRIGHTNESS	0
> +
> +struct wilco_keyboard_led_data {
> +	struct wilco_ec_device *ec;
> +	struct led_classdev keyboard;
> +};
> +
> +/* Send a request, get a response, and check that the response is good. */
> +static int send_kbbl_msg(struct wilco_ec_device *ec,
> +			 const struct wilco_ec_kbbl_msg *request,
> +			 struct wilco_ec_kbbl_msg *response)
> +{
> +	struct wilco_ec_message msg;
> +	int ret;
> +
> +	memset(&msg, 0, sizeof(msg));
> +	msg.type = WILCO_EC_MSG_LEGACY;
> +	msg.request_data = &request;
> +	msg.request_size = sizeof(request);
> +	msg.response_data = &response;
> +	msg.response_size = sizeof(response);
> +
> +	ret = wilco_ec_mailbox(ec, &msg);
> +	if (ret < 0)
> +		dev_err(ec->dev, "Failed sending brightness command: %d", ret);
> +
> +	if (response->status) {
> +		dev_err(ec->dev,
> +			"EC reported failure sending brightness command: %d",
> +			response->status);
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +/* This may sleep because it uses wilco_ec_mailbox() */
> +static int keyboard_led_set_brightness(struct led_classdev *cdev,
> +				       enum led_brightness brightness)
> +{
> +	struct wilco_ec_kbbl_msg request;
> +	struct wilco_ec_kbbl_msg response;
> +	struct wilco_keyboard_led_data *data;
> +
> +	memset(&request, 0, sizeof(request));
> +	request.command = WILCO_EC_COMMAND_KBBL;
> +	request.subcmd = WILCO_KBBL_SUBCMD_GET_STATE;
> +	request.mode = WILCO_KBBL_MODE_FLAG_PWM;
> +	request.percent = brightness;
> +
> +	data = container_of(cdev, struct wilco_keyboard_led_data, keyboard);
> +	return send_kbbl_msg(data->ec, &request, &response);
> +}
> +
> +/*
> + * Get the current brightness, ensuring that we are in PWM mode. If not
> + * in PWM mode, then the current brightness is meaningless, so set the
> + * brightness to KBBL_DEFAULT_BRIGHTNESS.
> + *
> + * Return: Final brightness of the keyboard, or negative error code on failure.
> + */
> +static int initialize_brightness(struct wilco_keyboard_led_data *data)
> +{
> +	struct wilco_ec_kbbl_msg request;
> +	struct wilco_ec_kbbl_msg response;
> +	int ret;
> +
> +	memset(&request, 0, sizeof(request));
> +	request.command = WILCO_EC_COMMAND_KBBL;
> +	request.subcmd = WILCO_KBBL_SUBCMD_GET_STATE;
> +
> +	ret = send_kbbl_msg(data->ec, &request, &response);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (response.mode & WILCO_KBBL_MODE_FLAG_PWM)
> +		return response.percent;
> +
> +	dev_warn(data->ec->dev, "Keyboard brightness not initialized by BIOS");
> +	ret = led_set_brightness_sync(&data->keyboard, KBBL_DEFAULT_BRIGHTNESS);
> +	if (ret < 0)
> +		return ret;
> +
> +	return KBBL_DEFAULT_BRIGHTNESS;
> +}
> +
> +static int keyboard_led_probe(struct platform_device *pdev)
> +{
> +	struct wilco_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
> +	struct wilco_keyboard_led_data *data;
> +	int ret;
> +
> +	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->ec = ec;
> +	/* This acts the same as the CrOS backlight, so use the same name */
> +	data->keyboard.name = "chromeos::kbd_backlight";
> +	data->keyboard.max_brightness = 100;
> +	data->keyboard.flags = LED_CORE_SUSPENDRESUME;
> +	data->keyboard.brightness_set_blocking = keyboard_led_set_brightness;
> +	ret = initialize_brightness(data);
> +	if (ret < 0)
> +		return ret;
> +	data->keyboard.brightness = ret;
> +
> +	ret = devm_led_classdev_register(&pdev->dev, &data->keyboard);
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +static struct platform_driver keyboard_led_driver = {
> +	.driver = {
> +		.name = DRV_NAME,
> +	},
> +	.probe = keyboard_led_probe,
> +};
> +module_platform_driver(keyboard_led_driver);
> +
> +MODULE_AUTHOR("Nick Crews <ncrews@chromium.org>");
> +MODULE_DESCRIPTION("Wilco keyboard backlight LED driver");
> +MODULE_LICENSE("GPL v2");
> +MODULE_ALIAS("platform:" DRV_NAME);
> diff --git a/include/linux/platform_data/wilco-ec.h b/include/linux/platform_data/wilco-ec.h
> index 1ff224793c99..c3965b7f397d 100644
> --- a/include/linux/platform_data/wilco-ec.h
> +++ b/include/linux/platform_data/wilco-ec.h
> @@ -32,6 +32,7 @@
>   * @data_size: Size of the data buffer used for EC communication.
>   * @debugfs_pdev: The child platform_device used by the debugfs sub-driver.
>   * @rtc_pdev: The child platform_device used by the RTC sub-driver.
> + * @kbbl_pdev: The child pdev used by the keyboard backlight sub-driver.
>   */
>  struct wilco_ec_device {
>  	struct device *dev;
> @@ -43,6 +44,7 @@ struct wilco_ec_device {
>  	size_t data_size;
>  	struct platform_device *debugfs_pdev;
>  	struct platform_device *rtc_pdev;
> +	struct platform_device *kbbl_pdev;
>  };
>  
>  /**
> @@ -114,6 +116,42 @@ struct wilco_ec_message {
>  	void *response_data;
>  };
>  
> +/* Constants and structs useful for keyboard backlight (KBBL) control */
> +
> +#define WILCO_EC_COMMAND_KBBL		0x75
> +#define WILCO_KBBL_MODE_FLAG_PWM	BIT(1)	/* Set brightness by percent. */
> +
> +/**
> + * enum kbbl_subcommand - What action does the EC perform?
> + * @WILCO_KBBL_SUBCMD_GET_FEATURES: Request available functionality from EC.
> + * @WILCO_KBBL_SUBCMD_GET_STATE: Request current mode and brightness from EC.
> + * @WILCO_KBBL_SUBCMD_SET_STATE: Write mode and brightness to EC.
> + */
> +enum kbbl_subcommand {
> +	WILCO_KBBL_SUBCMD_GET_FEATURES = 0x00,
> +	WILCO_KBBL_SUBCMD_GET_STATE = 0x01,
> +	WILCO_KBBL_SUBCMD_SET_STATE = 0x02,
> +};
> +
> +/**
> + * struct wilco_ec_kbbl_msg - Message to/from EC for keyboard backlight control.
> + * @command: Always WILCO_EC_COMMAND_KBBL.
> + * @status: Set by EC to 0 on success, 0xFF on failure.
> + * @subcmd: One of enum kbbl_subcommand.
> + * @mode: Bit flags for used mode, we want to use WILCO_KBBL_MODE_FLAG_PWM.
> + * @percent: Brightness in 0-100. Only meaningful in PWM mode.
> + */
> +struct wilco_ec_kbbl_msg {
> +	u8 command;
> +	u8 status;
> +	u8 subcmd;
> +	u8 reserved3;
> +	u8 mode;
> +	u8 reserved5to8[4];
> +	u8 percent;
> +	u8 reserved10to15[6];
> +} __packed;
> +
>  /**
>   * wilco_ec_mailbox() - Send request to the EC and receive the response.
>   * @ec: Wilco EC device.
>