Re: [PATCH v8 5/5] backlight: add led-backlight driver

[Sebastian Reichel]

Hi,

On Thu, Oct 03, 2019 at 10:28:12AM +0200, Jean-Jacques Hiblot wrote:
> From: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> 
> This patch adds a led-backlight driver (led_bl), which is similar to
> pwm_bl except the driver uses a LED class driver to adjust the
> brightness in the HW. Multiple LEDs can be used for a single backlight.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@xxxxxx>
> Acked-by: Pavel Machek <pavel@xxxxxx>
> Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>

(with some suggestions below)

>  drivers/video/backlight/Kconfig  |   7 +
>  drivers/video/backlight/Makefile |   1 +
>  drivers/video/backlight/led_bl.c | 260 +++++++++++++++++++++++++++++++
>  3 files changed, 268 insertions(+)
>  create mode 100644 drivers/video/backlight/led_bl.c
> 
> diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
> index 8b081d61773e..585a1787618c 100644
> --- a/drivers/video/backlight/Kconfig
> +++ b/drivers/video/backlight/Kconfig
> @@ -458,6 +458,13 @@ config BACKLIGHT_RAVE_SP
>  	help
>  	  Support for backlight control on RAVE SP device.
>  
> +config BACKLIGHT_LED
> +	tristate "Generic LED based Backlight Driver"
> +	depends on LEDS_CLASS && OF
> +	help
> +	  If you have a LCD backlight adjustable by LED class driver, say Y
> +	  to enable this driver.
> +
>  endif # BACKLIGHT_CLASS_DEVICE
>  
>  endmenu
> diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
> index 63c507c07437..2a67642966a5 100644
> --- a/drivers/video/backlight/Makefile
> +++ b/drivers/video/backlight/Makefile
> @@ -57,3 +57,4 @@ obj-$(CONFIG_BACKLIGHT_TPS65217)	+= tps65217_bl.o
>  obj-$(CONFIG_BACKLIGHT_WM831X)		+= wm831x_bl.o
>  obj-$(CONFIG_BACKLIGHT_ARCXCNN) 	+= arcxcnn_bl.o
>  obj-$(CONFIG_BACKLIGHT_RAVE_SP)		+= rave-sp-backlight.o
> +obj-$(CONFIG_BACKLIGHT_LED)		+= led_bl.o
> diff --git a/drivers/video/backlight/led_bl.c b/drivers/video/backlight/led_bl.c
> new file mode 100644
> index 000000000000..3f66549997c8
> --- /dev/null
> +++ b/drivers/video/backlight/led_bl.c
> @@ -0,0 +1,260 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2015-2019 Texas Instruments Incorporated -  http://www.ti.com/
> + * Author: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> + *
> + * Based on pwm_bl.c
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/leds.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +
> +struct led_bl_data {
> +	struct device		*dev;
> +	struct backlight_device	*bl_dev;
> +	struct led_classdev	**leds;
> +	bool			enabled;
> +	int			nb_leds;
> +	unsigned int		*levels;
> +	unsigned int		default_brightness;
> +	unsigned int		max_brightness;
> +};
> +
> +static void led_bl_set_brightness(struct led_bl_data *priv, int level)
> +{
> +	int i;
> +	int bkl_brightness;
> +
> +	if (priv->levels)
> +		bkl_brightness = priv->levels[level];
> +	else
> +		bkl_brightness = level;
> +
> +	for (i = 0; i < priv->nb_leds; i++)
> +		led_set_brightness(priv->leds[i], bkl_brightness);
> +
> +	priv->enabled = true;
> +}
> +
> +static void led_bl_power_off(struct led_bl_data *priv)
> +{
> +	int i;
> +
> +	if (!priv->enabled)
> +		return;
> +
> +	for (i = 0; i < priv->nb_leds; i++)
> +		led_set_brightness(priv->leds[i], LED_OFF);
> +
> +	priv->enabled = false;
> +}
> +
> +static int led_bl_update_status(struct backlight_device *bl)
> +{
> +	struct led_bl_data *priv = bl_get_data(bl);
> +	int brightness = bl->props.brightness;
> +
> +	if (bl->props.power != FB_BLANK_UNBLANK ||
> +	    bl->props.fb_blank != FB_BLANK_UNBLANK ||
> +	    bl->props.state & BL_CORE_FBBLANK)
> +		brightness = 0;
> +
> +	if (brightness > 0)
> +		led_bl_set_brightness(priv, brightness);
> +	else
> +		led_bl_power_off(priv);
> +
> +	return 0;
> +}
> +
> +static const struct backlight_ops led_bl_ops = {
> +	.update_status	= led_bl_update_status,
> +};
> +
> +static int led_bl_get_leds(struct device *dev,
> +			   struct led_bl_data *priv)
> +{
> +	int i, nb_leds, ret;
> +	struct device_node *node = dev->of_node;
> +	struct led_classdev **leds;
> +	unsigned int max_brightness;
> +	unsigned int default_brightness;
> +
> +	ret = of_count_phandle_with_args(node, "leds", NULL);
> +	if (ret < 0) {
> +		dev_err(dev, "Unable to get led count\n");
> +		return -EINVAL;
> +	}
> +
> +	nb_leds = ret;
> +	if (nb_leds < 1) {
> +		dev_err(dev, "At least one LED must be specified!\n");
> +		return -EINVAL;
> +	}
> +
> +	leds = devm_kzalloc(dev, sizeof(struct led_classdev *) * nb_leds,
> +			    GFP_KERNEL);
> +	if (!leds)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < nb_leds; i++) {
> +		leds[i] = devm_of_led_get(dev, i);
> +		if (IS_ERR(leds[i]))
> +			return PTR_ERR(leds[i]);
> +	}
> +
> +	/* check that the LEDs all have the same brightness range */
> +	max_brightness = leds[0]->max_brightness;
> +	for (i = 1; i < nb_leds; i++) {
> +		if (max_brightness != leds[i]->max_brightness) {
> +			dev_err(dev, "LEDs must have identical ranges\n");
> +			return -EINVAL;
> +		}
> +	}
> +
> +	/* get the default brightness from the first LED from the list */
> +	default_brightness = leds[0]->brightness;
> +
> +	priv->nb_leds = nb_leds;
> +	priv->leds = leds;
> +	priv->max_brightness = max_brightness;
> +	priv->default_brightness = default_brightness;
> +
> +	return 0;
> +}
> +
> +static int led_bl_parse_levels(struct device *dev,
> +			   struct led_bl_data *priv)
> +{
> +	struct device_node *node = dev->of_node;
> +	int num_levels;
> +	u32 value;
> +	int ret;
> +
> +	if (!node)
> +		return -ENODEV;
> +
> +	num_levels = of_property_count_u32_elems(node, "brightness-levels");
> +	if (num_levels > 1) {
> +		int i;
> +		unsigned int db;
> +		u32 *levels = NULL;
> +
> +		levels = devm_kzalloc(dev, sizeof(u32) * num_levels,
> +				      GFP_KERNEL);
> +		if (!levels)
> +			return -ENOMEM;
> +
> +		ret = of_property_read_u32_array(node, "brightness-levels",
> +						levels,
> +						num_levels);
> +		if (ret < 0)
> +			return ret;
> +
> +		/*
> +		 * Try to map actual LED brightness to backlight brightness
> +		 * level
> +		 */
> +		db = priv->default_brightness;
> +		for (i = 0 ; i < num_levels; i++) {
> +			if ((i && db > levels[i-1]) && db <= levels[i])
> +				break;
> +		}
> +		priv->default_brightness = i;
> +		priv->max_brightness = num_levels - 1;
> +		priv->levels = levels;
> +	} else if (num_levels >= 0)
> +		dev_warn(dev, "Not enough levels defined\n");
> +
> +	ret = of_property_read_u32(node, "default-brightness-level", &value);
> +	if (!ret && value <= priv->max_brightness)
> +		priv->default_brightness = value;
> +	else if (!ret  && value > priv->max_brightness)
> +		dev_warn(dev, "Invalid default brightness. Ignoring it\n");
> +
> +	return 0;
> +}
> +
> +static int led_bl_probe(struct platform_device *pdev)
> +{
> +	struct backlight_properties props;
> +	struct led_bl_data *priv;
> +	int ret, i;
> +
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, priv);
> +
> +	priv->dev = &pdev->dev;
> +
> +	ret = led_bl_get_leds(&pdev->dev, priv);
> +	if (ret)
> +		return ret;
> +
> +	ret = led_bl_parse_levels(&pdev->dev, priv);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "Failed to parse DT data\n");
> +		return ret;
> +	}
> +
> +	memset(&props, 0, sizeof(struct backlight_properties));
> +	props.type = BACKLIGHT_RAW;
> +	props.max_brightness = priv->max_brightness;
> +	props.brightness = priv->default_brightness;
> +	props.power = (priv->default_brightness > 0) ? FB_BLANK_POWERDOWN :
> +		      FB_BLANK_UNBLANK;
> +	priv->bl_dev = backlight_device_register(dev_name(&pdev->dev),
> +			&pdev->dev, priv, &led_bl_ops, &props);
> +	if (IS_ERR(priv->bl_dev)) {
> +		dev_err(&pdev->dev, "Failed to register backlight\n");
> +		return PTR_ERR(priv->bl_dev);
> +	}
> +
> +	for (i = 0; i < priv->nb_leds; i++)
> +		led_sysfs_disable(priv->leds[i]);

I suggest to restructure:

1. call led_sysfs_disable

2. use devm_add_action_or_reset() to register the
   led_sysfs_enable loop

3. use devm_backlight_device_register() to register BL

4. drop the remove function

> +
> +	backlight_update_status(priv->bl_dev);
> +
> +	return 0;
> +}
> +
> +static int led_bl_remove(struct platform_device *pdev)
> +{
> +	struct led_bl_data *priv = platform_get_drvdata(pdev);
> +	struct backlight_device *bl = priv->bl_dev;
> +	int i;
> +
> +	backlight_device_unregister(bl);
> +
> +	led_bl_power_off(priv);
> +	for (i = 0; i < priv->nb_leds; i++)
> +		led_sysfs_enable(priv->leds[i]);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id led_bl_of_match[] = {
> +	{ .compatible = "led-backlight" },
> +	{ }
> +};
> +
> +MODULE_DEVICE_TABLE(of, led_bl_of_match);
> +
> +static struct platform_driver led_bl_driver = {
> +	.driver		= {
> +		.name		= "led-backlight",
> +		.of_match_table	= of_match_ptr(led_bl_of_match),

You should drop of_match_ptr(). Since the driver depends on OF,
it will always simply return led_bl_of_match.

(Also after removing the OF dependency from the driver it would
either require led_bl_of_match to be marked __maybe_unused or
moving it into a #if CONFIG_OF area to avoid warnings.)

-- Sebastian

> +	},
> +	.probe		= led_bl_probe,
> +	.remove		= led_bl_remove,
> +};
> +
> +module_platform_driver(led_bl_driver);
> +
> +MODULE_DESCRIPTION("LED based Backlight Driver");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:led-backlight");
> -- 
> 2.17.1
> 
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