![Gustavo A. R. Silva](/assets/img/avatar_default.png)
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293
("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
200 lines
4.5 KiB
C
200 lines
4.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/drivers/leds-pwm.c
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*
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* simple PWM based LED control
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*
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* Copyright 2009 Luotao Fu @ Pengutronix (l.fu@pengutronix.de)
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*
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* based on leds-gpio.c by Raphael Assenat <raph@8d.com>
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*/
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/platform_device.h>
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#include <linux/of_platform.h>
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#include <linux/leds.h>
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#include <linux/err.h>
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#include <linux/pwm.h>
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#include <linux/slab.h>
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struct led_pwm {
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const char *name;
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const char *default_trigger;
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u8 active_low;
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unsigned int max_brightness;
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};
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struct led_pwm_platform_data {
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int num_leds;
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struct led_pwm *leds;
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};
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struct led_pwm_data {
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struct led_classdev cdev;
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struct pwm_device *pwm;
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struct pwm_state pwmstate;
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unsigned int active_low;
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};
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struct led_pwm_priv {
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int num_leds;
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struct led_pwm_data leds[];
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};
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static int led_pwm_set(struct led_classdev *led_cdev,
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enum led_brightness brightness)
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{
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struct led_pwm_data *led_dat =
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container_of(led_cdev, struct led_pwm_data, cdev);
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unsigned int max = led_dat->cdev.max_brightness;
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unsigned long long duty = led_dat->pwmstate.period;
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duty *= brightness;
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do_div(duty, max);
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if (led_dat->active_low)
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duty = led_dat->pwmstate.period - duty;
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led_dat->pwmstate.duty_cycle = duty;
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led_dat->pwmstate.enabled = duty > 0;
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return pwm_apply_state(led_dat->pwm, &led_dat->pwmstate);
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}
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static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
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struct led_pwm *led, struct fwnode_handle *fwnode)
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{
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struct led_pwm_data *led_data = &priv->leds[priv->num_leds];
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int ret;
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led_data->active_low = led->active_low;
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led_data->cdev.name = led->name;
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led_data->cdev.default_trigger = led->default_trigger;
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led_data->cdev.brightness = LED_OFF;
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led_data->cdev.max_brightness = led->max_brightness;
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led_data->cdev.flags = LED_CORE_SUSPENDRESUME;
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if (fwnode)
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led_data->pwm = devm_fwnode_pwm_get(dev, fwnode, NULL);
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else
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led_data->pwm = devm_pwm_get(dev, led->name);
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if (IS_ERR(led_data->pwm)) {
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ret = PTR_ERR(led_data->pwm);
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if (ret != -EPROBE_DEFER)
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dev_err(dev, "unable to request PWM for %s: %d\n",
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led->name, ret);
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return ret;
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}
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led_data->cdev.brightness_set_blocking = led_pwm_set;
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pwm_init_state(led_data->pwm, &led_data->pwmstate);
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ret = devm_led_classdev_register(dev, &led_data->cdev);
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if (ret == 0) {
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priv->num_leds++;
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led_pwm_set(&led_data->cdev, led_data->cdev.brightness);
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} else {
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dev_err(dev, "failed to register PWM led for %s: %d\n",
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led->name, ret);
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}
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return ret;
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}
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static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
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{
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struct fwnode_handle *fwnode;
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struct led_pwm led;
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int ret = 0;
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memset(&led, 0, sizeof(led));
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device_for_each_child_node(dev, fwnode) {
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ret = fwnode_property_read_string(fwnode, "label", &led.name);
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if (ret && is_of_node(fwnode))
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led.name = to_of_node(fwnode)->name;
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if (!led.name) {
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fwnode_handle_put(fwnode);
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return -EINVAL;
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}
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fwnode_property_read_string(fwnode, "linux,default-trigger",
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&led.default_trigger);
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led.active_low = fwnode_property_read_bool(fwnode,
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"active-low");
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fwnode_property_read_u32(fwnode, "max-brightness",
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&led.max_brightness);
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ret = led_pwm_add(dev, priv, &led, fwnode);
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if (ret) {
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fwnode_handle_put(fwnode);
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break;
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}
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}
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return ret;
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}
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static int led_pwm_probe(struct platform_device *pdev)
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{
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struct led_pwm_platform_data *pdata = dev_get_platdata(&pdev->dev);
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struct led_pwm_priv *priv;
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int count, i;
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int ret = 0;
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if (pdata)
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count = pdata->num_leds;
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else
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count = device_get_child_node_count(&pdev->dev);
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if (!count)
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return -EINVAL;
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priv = devm_kzalloc(&pdev->dev, struct_size(priv, leds, count),
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GFP_KERNEL);
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if (!priv)
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return -ENOMEM;
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if (pdata) {
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for (i = 0; i < count; i++) {
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ret = led_pwm_add(&pdev->dev, priv, &pdata->leds[i],
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NULL);
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if (ret)
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break;
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}
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} else {
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ret = led_pwm_create_fwnode(&pdev->dev, priv);
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}
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if (ret)
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return ret;
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platform_set_drvdata(pdev, priv);
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return 0;
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}
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static const struct of_device_id of_pwm_leds_match[] = {
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{ .compatible = "pwm-leds", },
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{},
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};
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MODULE_DEVICE_TABLE(of, of_pwm_leds_match);
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static struct platform_driver led_pwm_driver = {
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.probe = led_pwm_probe,
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.driver = {
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.name = "leds_pwm",
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.of_match_table = of_pwm_leds_match,
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},
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};
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module_platform_driver(led_pwm_driver);
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MODULE_AUTHOR("Luotao Fu <l.fu@pengutronix.de>");
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MODULE_DESCRIPTION("generic PWM LED driver");
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MODULE_LICENSE("GPL v2");
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MODULE_ALIAS("platform:leds-pwm");
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