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| 1 | #include <linux/kernel.h> |
| 2 | #include <linux/platform_device.h> |
| 3 | #include <linux/leds.h> |
| 4 | #include <linux/io.h> |
| 5 | #include <linux/atmel_pwm.h> |
| 6 | #include <linux/slab.h> |
| 7 | #include <linux/module.h> |
| 8 | |
| 9 | |
| 10 | struct pwmled { |
| 11 | struct led_classdev cdev; |
| 12 | struct pwm_channel pwmc; |
| 13 | struct gpio_led *desc; |
| 14 | u32 mult; |
| 15 | u8 active_low; |
| 16 | }; |
| 17 | |
| 18 | |
| 19 | /* |
| 20 | * For simplicity, we use "brightness" as if it were a linear function |
| 21 | * of PWM duty cycle. However, a logarithmic function of duty cycle is |
| 22 | * probably a better match for perceived brightness: two is half as bright |
| 23 | * as four, four is half as bright as eight, etc |
| 24 | */ |
| 25 | static void pwmled_brightness(struct led_classdev *cdev, enum led_brightness b) |
| 26 | { |
| 27 | struct pwmled *led; |
| 28 | |
| 29 | /* update the duty cycle for the *next* period */ |
| 30 | led = container_of(cdev, struct pwmled, cdev); |
| 31 | pwm_channel_writel(&led->pwmc, PWM_CUPD, led->mult * (unsigned) b); |
| 32 | } |
| 33 | |
| 34 | /* |
| 35 | * NOTE: we reuse the platform_data structure of GPIO leds, |
| 36 | * but repurpose its "gpio" number as a PWM channel number. |
| 37 | */ |
| 38 | static int pwmled_probe(struct platform_device *pdev) |
| 39 | { |
| 40 | const struct gpio_led_platform_data *pdata; |
| 41 | struct pwmled *leds; |
| 42 | int i; |
| 43 | int status; |
| 44 | |
| 45 | pdata = pdev->dev.platform_data; |
| 46 | if (!pdata || pdata->num_leds < 1) |
| 47 | return -ENODEV; |
| 48 | |
| 49 | leds = devm_kzalloc(&pdev->dev, pdata->num_leds * sizeof(*leds), |
| 50 | GFP_KERNEL); |
| 51 | if (!leds) |
| 52 | return -ENOMEM; |
| 53 | |
| 54 | for (i = 0; i < pdata->num_leds; i++) { |
| 55 | struct pwmled *led = leds + i; |
| 56 | const struct gpio_led *dat = pdata->leds + i; |
| 57 | u32 tmp; |
| 58 | |
| 59 | led->cdev.name = dat->name; |
| 60 | led->cdev.brightness = LED_OFF; |
| 61 | led->cdev.brightness_set = pwmled_brightness; |
| 62 | led->cdev.default_trigger = dat->default_trigger; |
| 63 | |
| 64 | led->active_low = dat->active_low; |
| 65 | |
| 66 | status = pwm_channel_alloc(dat->gpio, &led->pwmc); |
| 67 | if (status < 0) |
| 68 | goto err; |
| 69 | |
| 70 | /* |
| 71 | * Prescale clock by 2^x, so PWM counts in low MHz. |
| 72 | * Start each cycle with the LED active, so increasing |
| 73 | * the duty cycle gives us more time on (== brighter). |
| 74 | */ |
| 75 | tmp = 5; |
| 76 | if (!led->active_low) |
| 77 | tmp |= PWM_CPR_CPOL; |
| 78 | pwm_channel_writel(&led->pwmc, PWM_CMR, tmp); |
| 79 | |
| 80 | /* |
| 81 | * Pick a period so PWM cycles at 100+ Hz; and a multiplier |
| 82 | * for scaling duty cycle: brightness * mult. |
| 83 | */ |
| 84 | tmp = (led->pwmc.mck / (1 << 5)) / 100; |
| 85 | tmp /= 255; |
| 86 | led->mult = tmp; |
| 87 | pwm_channel_writel(&led->pwmc, PWM_CDTY, |
| 88 | led->cdev.brightness * 255); |
| 89 | pwm_channel_writel(&led->pwmc, PWM_CPRD, |
| 90 | LED_FULL * tmp); |
| 91 | |
| 92 | pwm_channel_enable(&led->pwmc); |
| 93 | |
| 94 | /* Hand it over to the LED framework */ |
| 95 | status = led_classdev_register(&pdev->dev, &led->cdev); |
| 96 | if (status < 0) { |
| 97 | pwm_channel_free(&led->pwmc); |
| 98 | goto err; |
| 99 | } |
| 100 | } |
| 101 | |
| 102 | platform_set_drvdata(pdev, leds); |
| 103 | return 0; |
| 104 | |
| 105 | err: |
| 106 | if (i > 0) { |
| 107 | for (i = i - 1; i >= 0; i--) { |
| 108 | led_classdev_unregister(&leds[i].cdev); |
| 109 | pwm_channel_free(&leds[i].pwmc); |
| 110 | } |
| 111 | } |
| 112 | |
| 113 | return status; |
| 114 | } |
| 115 | |
| 116 | static int __exit pwmled_remove(struct platform_device *pdev) |
| 117 | { |
| 118 | const struct gpio_led_platform_data *pdata; |
| 119 | struct pwmled *leds; |
| 120 | unsigned i; |
| 121 | |
| 122 | pdata = pdev->dev.platform_data; |
| 123 | leds = platform_get_drvdata(pdev); |
| 124 | |
| 125 | for (i = 0; i < pdata->num_leds; i++) { |
| 126 | struct pwmled *led = leds + i; |
| 127 | |
| 128 | led_classdev_unregister(&led->cdev); |
| 129 | pwm_channel_free(&led->pwmc); |
| 130 | } |
| 131 | |
| 132 | platform_set_drvdata(pdev, NULL); |
| 133 | return 0; |
| 134 | } |
| 135 | |
| 136 | static struct platform_driver pwmled_driver = { |
| 137 | .driver = { |
| 138 | .name = "leds-atmel-pwm", |
| 139 | .owner = THIS_MODULE, |
| 140 | }, |
| 141 | /* REVISIT add suspend() and resume() methods */ |
| 142 | .probe = pwmled_probe, |
| 143 | .remove = __exit_p(pwmled_remove), |
| 144 | }; |
| 145 | |
| 146 | module_platform_driver(pwmled_driver); |
| 147 | |
| 148 | MODULE_DESCRIPTION("Driver for LEDs with PWM-controlled brightness"); |
| 149 | MODULE_LICENSE("GPL"); |
| 150 | MODULE_ALIAS("platform:leds-atmel-pwm"); |
| 151 |
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Tags:
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