Re: [PATCH 3/4] backlight: add led-backlight driver
From: Jean-Jacques Hiblot
Date: Wed Jul 03 2019 - 06:02:41 EST
Daniel,
On 03/07/2019 11:44, Daniel Thompson wrote:
On Tue, Jul 02, 2019 at 05:17:21PM +0200, Jean-Jacques Hiblot wrote:
Daniel,
On 02/07/2019 15:04, Daniel Thompson wrote:
On Tue, Jul 02, 2019 at 12:59:53PM +0200, Jean-Jacques Hiblot wrote:
Hi Daniel,
On 02/07/2019 11:54, Daniel Thompson wrote:
On Mon, Jul 01, 2019 at 05:14:22PM +0200, Jean-Jacques Hiblot wrote:
From: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
This patch adds a led-backlight driver (led_bl), which is mostly similar to
pwm_bl except the driver uses a LED class driver to adjust the brightness
in the HW.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@xxxxxx>
---
drivers/video/backlight/Kconfig | 7 +
drivers/video/backlight/Makefile | 1 +
drivers/video/backlight/led_bl.c | 217 +++++++++++++++++++++++++++++++
3 files changed, 225 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..e699924cc2bc
--- /dev/null
+++ b/drivers/video/backlight/led_bl.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2018 Texas Instruments Incorporated - http://www.ti.com/
+ * Author: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
+ *
+ * Based on pwm_bl.c
+ */
+
+#include <linux/backlight.h>
+#include <linux/gpio/consumer.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+struct led_bl_data {
+ struct device *dev;
+ struct backlight_device *bl_dev;
+
+ unsigned int *levels;
+ bool enabled;
+ struct regulator *power_supply;
+ struct gpio_desc *enable_gpio;
For the PWM driver the power_supply and enable_gpio are part of managing
a dumb LED driver device that is downstream of the PWM.
What is their purpose when we wrap an LED device? Put another why why isn't
the LED device driver responsible for this?
This question came up when the patch was first proposed in 2015. Here is the
answer from Tomi at the time. It is still relevant.
"These are for the backlight, not for the LED chip. So "LED" here is a
chip that produces (most likely) a PWM signal, and "backlight" is the
collection of components that use the PWM to produce the backlight
itself, and use the power-supply and gpios."
Expanded significantly in the associated thread, right?
https://patchwork.kernel.org/patch/7293991/
Also still relevant is whether the LED device is being correctly
modelled if the act of turning on the LED doesn't, in fact, turn the LED
on. Is it *really* a correct implementation of an LED device that
setting it to LED_FULL using sysfs doesn't cause it to light up?
What I understood from the discussion between Rob and Tomi is that the
child-node of the LED controller should be considered a backlight device,
not a simple LED. I'm not sure if the sysfs interface is still relevant in
that case. Maybe it should just be disabled by the backlight driver
(possible with led_sysfs_disable())
led_sysfs_disable() sounds like a sensible change but that's not quite
what I mean.
It is more a thought experiment to see if the power control *should* be
implemented by the backlight. Consider what happens if we *don't*
enable CONFIG_BACKLIGHT_LED in the kernel: we would still have an LED
device and it would not work correctly.
In other words I naively expect turning on an LED using the LED API
(any of them, sysfs or kernel) to result in the LED turning on.
Implementing a workaround in the client for what appears to be
something missing in the LED driver strikes me as odd. Why shouldn't
the regulator be managed in the LED driver?
I see your point. Indeed having the regulator handled in the LED-core
makes sense in a lot of situations
I'll think about it.
Actually there is another area where I think an LED backlight should
perhaps be held to a higher standard than a PWM backlight and that is
handling backlights composed of multiple LEDs.
Using the TLC591xx examples from the thread above... these are
multi-channel (8 or 16) LED controllers and I don't think its
speculative to assume that a backlight could constructed using
one of these could require multiple LEDs.
In that case, the device-tree model must be quite different.
Actually the best way to do that is to use the model from Tomi
https://patchwork.kernel.org/patch/7293991/ and modify it to handle more
than one LED
<https://patchwork.kernel.org/patch/7293991/>
I'm not completely sure that people would start making real backlight this
way though. It is much more probable that the ouput of the led ctrl is
connected to a single control input of a real backlight than to actual LEDs.
I'm afraid I don't follow this. If you have a backlight composed of mutliple
strings why wouldn't each string be attached directly to the output an of LED
driver chip such as the TLC591xx family.
OK. It makes sense.
I'll rework the series in this direction: multiple LED devices handled
by one backlight device
Thanks,
JJ
Daniel.
JJ
Daniel.
+
+ struct led_classdev *led_cdev;
+
+ unsigned int max_brightness;
+ unsigned int default_brightness;
+};
+
+static void led_bl_set_brightness(struct led_bl_data *priv, int brightness)
+{
+ int err;
+
+ if (!priv->enabled) {
+ err = regulator_enable(priv->power_supply);
+ if (err < 0)
+ dev_err(priv->dev, "failed to enable power supply\n");
+
+ if (priv->enable_gpio)
+ gpiod_set_value_cansleep(priv->enable_gpio, 1);
+ }
+
+ led_set_brightness(priv->led_cdev, priv->levels[brightness]);
+
+ priv->enabled = true;
+}
+
+static void led_bl_power_off(struct led_bl_data *priv)
+{
+ if (!priv->enabled)
+ return;
+
+ led_set_brightness(priv->led_cdev, LED_OFF);
+
+ if (priv->enable_gpio)
+ gpiod_set_value_cansleep(priv->enable_gpio, 0);
+
+ regulator_disable(priv->power_supply);
+
+ 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_parse_dt(struct device *dev,
+ struct led_bl_data *priv)
+{
+ struct device_node *node = dev->of_node;
+ int num_levels;
+ u32 *levels;
+ u32 value;
+ int ret;
+
+ if (!node)
+ return -ENODEV;
+
+ num_levels = of_property_count_u32_elems(node, "brightness-levels");
Is there any reason that this function cannot use the (more generic)
device property API throughout this function?
No reason. The code is a bit old, and can do with an update.
Are you thinking of of_property_read_u32_array(), or another function ?
JJ
Daniel.
+ if (num_levels < 0)
+ return num_levels;
+
+ 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;
+
+ ret = of_property_read_u32(node, "default-brightness-level", &value);
+ if (ret < 0)
+ return ret;
+
+ if (value >= num_levels) {
+ dev_err(dev, "invalid default-brightness-level\n");
+ return -EINVAL;
+ }
+
+ priv->levels = levels;
+ priv->max_brightness = num_levels - 1;
+ priv->default_brightness = value;
+
+ return 0;
+}
+
+static int led_bl_probe(struct platform_device *pdev)
+{
+ struct backlight_properties props;
+ struct led_bl_data *priv;
+ int ret;
+
+ priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+ if (!priv)
+ return -ENOMEM;
+
+ platform_set_drvdata(pdev, priv);
+
+ priv->dev = &pdev->dev;
+ priv->led_cdev = to_led_classdev(pdev->dev.parent);
+
+ ret = led_bl_parse_dt(&pdev->dev, priv);
+ if (ret < 0) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(&pdev->dev, "failed to parse DT data\n");
+ return ret;
+ }
+
+ priv->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
+ GPIOD_OUT_LOW);
+ if (IS_ERR(priv->enable_gpio)) {
+ ret = PTR_ERR(priv->enable_gpio);
+ goto err;
+ }
+
+ priv->power_supply = devm_regulator_get(&pdev->dev, "power");
+ if (IS_ERR(priv->power_supply)) {
+ ret = PTR_ERR(priv->power_supply);
+ goto err;
+ }
+
+ memset(&props, 0, sizeof(struct backlight_properties));
+ props.type = BACKLIGHT_RAW;
+ props.max_brightness = priv->max_brightness;
+ 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");
+ ret = PTR_ERR(priv->bl_dev);
+ goto err;
+ }
+
+ priv->bl_dev->props.brightness = priv->default_brightness;
+ backlight_update_status(priv->bl_dev);
+
+ return 0;
+
+err:
+
+ return ret;
+}
+
+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;
+
+ backlight_device_unregister(bl);
+
+ led_bl_power_off(priv);
+
+ 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),
+ },
+ .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