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| 1 | +// SPDX-License-Identifier: GPL-2.0-only |
| 2 | +/* |
| 3 | + * Backlight driver for the Kinetic KTD253 |
| 4 | + * Based on code and know-how from the Samsung GT-S7710 |
| 5 | + * Gareth Phillips <[email protected]> |
| 6 | + */ |
| 7 | +#include <linux/backlight.h> |
| 8 | +#include <linux/delay.h> |
| 9 | +#include <linux/err.h> |
| 10 | +#include <linux/fb.h> |
| 11 | +#include <linux/gpio/consumer.h> |
| 12 | +#include <linux/init.h> |
| 13 | +#include <linux/kernel.h> |
| 14 | +#include <linux/limits.h> |
| 15 | +#include <linux/module.h> |
| 16 | +#include <linux/of.h> |
| 17 | +#include <linux/platform_device.h> |
| 18 | +#include <linux/property.h> |
| 19 | +#include <linux/slab.h> |
| 20 | + |
| 21 | +/* Current ratio is n/32 from 1/32 to 32/32 */ |
| 22 | +#define KTD253_MIN_RATIO 1 |
| 23 | +#define KTD253_MAX_RATIO 32 |
| 24 | +#define KTD253_DEFAULT_RATIO 13 |
| 25 | + |
| 26 | +#define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */ |
| 27 | +#define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */ |
| 28 | +#define KTD253_T_OFF_MS 3 |
| 29 | + |
| 30 | +struct ktd253_backlight { |
| 31 | + struct device *dev; |
| 32 | + struct backlight_device *bl; |
| 33 | + struct gpio_desc *gpiod; |
| 34 | + u16 ratio; |
| 35 | +}; |
| 36 | + |
| 37 | +static int ktd253_backlight_update_status(struct backlight_device *bl) |
| 38 | +{ |
| 39 | + struct ktd253_backlight *ktd253 = bl_get_data(bl); |
| 40 | + int brightness = backlight_get_brightness(bl); |
| 41 | + u16 target_ratio; |
| 42 | + u16 current_ratio = ktd253->ratio; |
| 43 | + unsigned long flags; |
| 44 | + |
| 45 | + dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness); |
| 46 | + |
| 47 | + target_ratio = brightness; |
| 48 | + |
| 49 | + if (target_ratio == current_ratio) |
| 50 | + /* This is already right */ |
| 51 | + return 0; |
| 52 | + |
| 53 | + if (target_ratio == 0) { |
| 54 | + gpiod_set_value_cansleep(ktd253->gpiod, 0); |
| 55 | + /* |
| 56 | + * We need to keep the GPIO low for at least this long |
| 57 | + * to actually switch the KTD253 off. |
| 58 | + */ |
| 59 | + msleep(KTD253_T_OFF_MS); |
| 60 | + ktd253->ratio = 0; |
| 61 | + return 0; |
| 62 | + } |
| 63 | + |
| 64 | + if (current_ratio == 0) { |
| 65 | + gpiod_set_value_cansleep(ktd253->gpiod, 1); |
| 66 | + ndelay(KTD253_T_HIGH_NS); |
| 67 | + /* We always fall back to this when we power on */ |
| 68 | + current_ratio = KTD253_MAX_RATIO; |
| 69 | + } |
| 70 | + |
| 71 | + /* |
| 72 | + * WARNING: |
| 73 | + * The loop to set the correct current level is performed |
| 74 | + * with interrupts disabled as it is timing critical. |
| 75 | + * The maximum number of cycles of the loop is 32 |
| 76 | + * so the time taken will be (T_LOW_NS + T_HIGH_NS + loop_time) * 32, |
| 77 | + */ |
| 78 | + local_irq_save(flags); |
| 79 | + while (current_ratio != target_ratio) { |
| 80 | + /* |
| 81 | + * These GPIO operations absolutely can NOT sleep so no |
| 82 | + * _cansleep suffixes, and no using GPIO expanders on |
| 83 | + * slow buses for this! |
| 84 | + */ |
| 85 | + gpiod_set_value(ktd253->gpiod, 0); |
| 86 | + ndelay(KTD253_T_LOW_NS); |
| 87 | + gpiod_set_value(ktd253->gpiod, 1); |
| 88 | + ndelay(KTD253_T_HIGH_NS); |
| 89 | + /* After 1/32 we loop back to 32/32 */ |
| 90 | + if (current_ratio == KTD253_MIN_RATIO) |
| 91 | + current_ratio = KTD253_MAX_RATIO; |
| 92 | + else |
| 93 | + current_ratio--; |
| 94 | + } |
| 95 | + local_irq_restore(flags); |
| 96 | + ktd253->ratio = current_ratio; |
| 97 | + |
| 98 | + dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio); |
| 99 | + |
| 100 | + return 0; |
| 101 | +} |
| 102 | + |
| 103 | +static const struct backlight_ops ktd253_backlight_ops = { |
| 104 | + .options = BL_CORE_SUSPENDRESUME, |
| 105 | + .update_status = ktd253_backlight_update_status, |
| 106 | +}; |
| 107 | + |
| 108 | +static int ktd253_backlight_probe(struct platform_device *pdev) |
| 109 | +{ |
| 110 | + struct device *dev = &pdev->dev; |
| 111 | + struct backlight_device *bl; |
| 112 | + struct ktd253_backlight *ktd253; |
| 113 | + u32 max_brightness; |
| 114 | + u32 brightness; |
| 115 | + int ret; |
| 116 | + |
| 117 | + ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL); |
| 118 | + if (!ktd253) |
| 119 | + return -ENOMEM; |
| 120 | + ktd253->dev = dev; |
| 121 | + |
| 122 | + ret = device_property_read_u32(dev, "max-brightness", &max_brightness); |
| 123 | + if (ret) |
| 124 | + max_brightness = KTD253_MAX_RATIO; |
| 125 | + if (max_brightness > KTD253_MAX_RATIO) { |
| 126 | + /* Clamp brightness to hardware max */ |
| 127 | + dev_err(dev, "illegal max brightness specified\n"); |
| 128 | + max_brightness = KTD253_MAX_RATIO; |
| 129 | + } |
| 130 | + |
| 131 | + ret = device_property_read_u32(dev, "default-brightness", &brightness); |
| 132 | + if (ret) |
| 133 | + brightness = KTD253_DEFAULT_RATIO; |
| 134 | + if (brightness > max_brightness) { |
| 135 | + /* Clamp default brightness to max brightness */ |
| 136 | + dev_err(dev, "default brightness exceeds max brightness\n"); |
| 137 | + brightness = max_brightness; |
| 138 | + } |
| 139 | + |
| 140 | + if (brightness) |
| 141 | + /* This will be the default ratio when the KTD253 is enabled */ |
| 142 | + ktd253->ratio = KTD253_MAX_RATIO; |
| 143 | + else |
| 144 | + ktd253->ratio = 0; |
| 145 | + |
| 146 | + ktd253->gpiod = devm_gpiod_get(dev, "enable", |
| 147 | + brightness ? GPIOD_OUT_HIGH : |
| 148 | + GPIOD_OUT_LOW); |
| 149 | + if (IS_ERR(ktd253->gpiod)) { |
| 150 | + ret = PTR_ERR(ktd253->gpiod); |
| 151 | + if (ret != -EPROBE_DEFER) |
| 152 | + dev_err(dev, "gpio line missing or invalid.\n"); |
| 153 | + return ret; |
| 154 | + } |
| 155 | + gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev)); |
| 156 | + |
| 157 | + bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253, |
| 158 | + &ktd253_backlight_ops, NULL); |
| 159 | + if (IS_ERR(bl)) { |
| 160 | + dev_err(dev, "failed to register backlight\n"); |
| 161 | + return PTR_ERR(bl); |
| 162 | + } |
| 163 | + bl->props.max_brightness = max_brightness; |
| 164 | + /* When we just enable the GPIO line we set max brightness */ |
| 165 | + if (brightness) { |
| 166 | + bl->props.brightness = brightness; |
| 167 | + bl->props.power = FB_BLANK_UNBLANK; |
| 168 | + } else { |
| 169 | + bl->props.brightness = 0; |
| 170 | + bl->props.power = FB_BLANK_POWERDOWN; |
| 171 | + } |
| 172 | + |
| 173 | + ktd253->bl = bl; |
| 174 | + platform_set_drvdata(pdev, bl); |
| 175 | + backlight_update_status(bl); |
| 176 | + |
| 177 | + return 0; |
| 178 | +} |
| 179 | + |
| 180 | +static const struct of_device_id ktd253_backlight_of_match[] = { |
| 181 | + { .compatible = "kinetic,ktd253" }, |
| 182 | + { /* sentinel */ } |
| 183 | +}; |
| 184 | +MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match); |
| 185 | + |
| 186 | +static struct platform_driver ktd253_backlight_driver = { |
| 187 | + .driver = { |
| 188 | + .name = "ktd253-backlight", |
| 189 | + .of_match_table = ktd253_backlight_of_match, |
| 190 | + }, |
| 191 | + .probe = ktd253_backlight_probe, |
| 192 | +}; |
| 193 | +module_platform_driver(ktd253_backlight_driver); |
| 194 | + |
| 195 | +MODULE_AUTHOR( "Linus Walleij <[email protected]>"); |
| 196 | +MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver"); |
| 197 | +MODULE_LICENSE("GPL"); |
| 198 | +MODULE_ALIAS("platform:ktd253-backlight"); |
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