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![Stefan Agner](/assets/img/avatar_default.png)
There are situations where the backlight should be on at boot time (e.g. if the boot loader already turned the display on). The DT bindings specify the "default-on" property for that purpose. Currently, the initial state of the GPIO at request time is always set to logical off (high or low depending on whether it is an active high or low GPIO). Since the GPIO is requested as an output, the GPIO will be driven low for a short period of time, which leads to a flickering display in the above use-case. Initialize the GPIO depending on the default-on property to be logical on or off. Signed-off-by: Stefan Agner <stefan@agner.ch> Signed-off-by: Lee Jones <lee.jones@linaro.org>
170 lines
4.2 KiB
C
170 lines
4.2 KiB
C
/*
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* gpio_backlight.c - Simple GPIO-controlled backlight
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/backlight.h>
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#include <linux/err.h>
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#include <linux/fb.h>
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#include <linux/gpio.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/of.h>
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#include <linux/of_gpio.h>
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#include <linux/platform_data/gpio_backlight.h>
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#include <linux/platform_device.h>
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#include <linux/slab.h>
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struct gpio_backlight {
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struct device *dev;
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struct device *fbdev;
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int gpio;
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int active;
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int def_value;
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};
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static int gpio_backlight_update_status(struct backlight_device *bl)
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{
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struct gpio_backlight *gbl = bl_get_data(bl);
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int brightness = bl->props.brightness;
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if (bl->props.power != FB_BLANK_UNBLANK ||
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bl->props.fb_blank != FB_BLANK_UNBLANK ||
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bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
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brightness = 0;
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gpio_set_value_cansleep(gbl->gpio,
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brightness ? gbl->active : !gbl->active);
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return 0;
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}
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static int gpio_backlight_check_fb(struct backlight_device *bl,
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struct fb_info *info)
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{
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struct gpio_backlight *gbl = bl_get_data(bl);
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return gbl->fbdev == NULL || gbl->fbdev == info->dev;
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}
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static const struct backlight_ops gpio_backlight_ops = {
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.options = BL_CORE_SUSPENDRESUME,
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.update_status = gpio_backlight_update_status,
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.check_fb = gpio_backlight_check_fb,
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};
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static int gpio_backlight_probe_dt(struct platform_device *pdev,
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struct gpio_backlight *gbl)
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{
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struct device_node *np = pdev->dev.of_node;
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enum of_gpio_flags gpio_flags;
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gbl->gpio = of_get_gpio_flags(np, 0, &gpio_flags);
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if (!gpio_is_valid(gbl->gpio)) {
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if (gbl->gpio != -EPROBE_DEFER) {
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dev_err(&pdev->dev,
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"Error: The gpios parameter is missing or invalid.\n");
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}
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return gbl->gpio;
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}
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gbl->active = (gpio_flags & OF_GPIO_ACTIVE_LOW) ? 0 : 1;
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gbl->def_value = of_property_read_bool(np, "default-on");
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return 0;
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}
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static int gpio_backlight_probe(struct platform_device *pdev)
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{
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struct gpio_backlight_platform_data *pdata =
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dev_get_platdata(&pdev->dev);
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struct backlight_properties props;
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struct backlight_device *bl;
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struct gpio_backlight *gbl;
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struct device_node *np = pdev->dev.of_node;
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unsigned long flags = GPIOF_DIR_OUT;
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int ret;
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if (!pdata && !np) {
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dev_err(&pdev->dev,
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"failed to find platform data or device tree node.\n");
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return -ENODEV;
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}
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gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
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if (gbl == NULL)
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return -ENOMEM;
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gbl->dev = &pdev->dev;
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if (np) {
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ret = gpio_backlight_probe_dt(pdev, gbl);
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if (ret)
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return ret;
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} else {
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gbl->fbdev = pdata->fbdev;
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gbl->gpio = pdata->gpio;
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gbl->active = pdata->active_low ? 0 : 1;
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gbl->def_value = pdata->def_value;
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}
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if (gbl->active)
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flags |= gbl->def_value ? GPIOF_INIT_HIGH : GPIOF_INIT_LOW;
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else
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flags |= gbl->def_value ? GPIOF_INIT_LOW : GPIOF_INIT_HIGH;
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ret = devm_gpio_request_one(gbl->dev, gbl->gpio, flags,
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pdata ? pdata->name : "backlight");
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if (ret < 0) {
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dev_err(&pdev->dev, "unable to request GPIO\n");
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return ret;
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}
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memset(&props, 0, sizeof(props));
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props.type = BACKLIGHT_RAW;
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props.max_brightness = 1;
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bl = devm_backlight_device_register(&pdev->dev, dev_name(&pdev->dev),
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&pdev->dev, gbl, &gpio_backlight_ops,
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&props);
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if (IS_ERR(bl)) {
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dev_err(&pdev->dev, "failed to register backlight\n");
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return PTR_ERR(bl);
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}
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bl->props.brightness = gbl->def_value;
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backlight_update_status(bl);
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platform_set_drvdata(pdev, bl);
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return 0;
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}
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#ifdef CONFIG_OF
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static struct of_device_id gpio_backlight_of_match[] = {
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{ .compatible = "gpio-backlight" },
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(of, gpio_backlight_of_match);
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#endif
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static struct platform_driver gpio_backlight_driver = {
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.driver = {
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.name = "gpio-backlight",
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.of_match_table = of_match_ptr(gpio_backlight_of_match),
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},
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.probe = gpio_backlight_probe,
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};
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module_platform_driver(gpio_backlight_driver);
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MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
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MODULE_DESCRIPTION("GPIO-based Backlight Driver");
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MODULE_LICENSE("GPL");
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MODULE_ALIAS("platform:gpio-backlight");
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