drivers/video/backlight/ktd253-backlight.c

   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 <gareth.phillips@samsung.com>
   6  */
   7 #include <linux/backlight.h>
   8 #include <linux/delay.h>
   9 #include <linux/err.h>
  10 #include <linux/gpio/consumer.h>
  11 #include <linux/init.h>
  12 #include <linux/kernel.h>
  13 #include <linux/limits.h>
  14 #include <linux/module.h>
  15 #include <linux/of.h>
  16 #include <linux/platform_device.h>
  17 #include <linux/property.h>
  18 #include <linux/slab.h>
  19
  20 /* Current ratio is n/32 from 1/32 to 32/32 */
  21 #define KTD253_MIN_RATIO 1
  22 #define KTD253_MAX_RATIO 32
  23 #define KTD253_DEFAULT_RATIO 13
  24
  25 #define KTD253_T_LOW_NS (200 + 10) /* Additional 10ns as safety factor */
  26 #define KTD253_T_HIGH_NS (200 + 10) /* Additional 10ns as safety factor */
  27 #define KTD253_T_OFF_CRIT_NS 100000 /* 100 us, now it doesn't look good */
  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 void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253)
  38 {
  39         gpiod_set_value_cansleep(ktd253->gpiod, 1);
  40         ndelay(KTD253_T_HIGH_NS);
  41         /* We always fall back to this when we power on */
  42 }
  43
  44 static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253)
  45 {
  46         /*
  47          * These GPIO operations absolutely can NOT sleep so no _cansleep
  48          * suffixes, and no using GPIO expanders on slow buses for this!
  49          *
  50          * The maximum number of cycles of the loop is 32  so the time taken
  51          * should nominally be:
  52          * (T_LOW_NS + T_HIGH_NS + loop_time) * 32
  53          *
  54          * Architectures do not always support ndelay() and we will get a few us
  55          * instead. If we get to a critical time limit an interrupt has likely
  56          * occured in the low part of the loop and we need to restart from the
  57          * top so we have the backlight in a known state.
  58          */
  59         u64 ns;
  60
  61         ns = ktime_get_ns();
  62         gpiod_set_value(ktd253->gpiod, 0);
  63         ndelay(KTD253_T_LOW_NS);
  64         gpiod_set_value(ktd253->gpiod, 1);
  65         ns = ktime_get_ns() - ns;
  66         if (ns >= KTD253_T_OFF_CRIT_NS) {
  67                 dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns);
  68                 return -EAGAIN;
  69         }
  70         ndelay(KTD253_T_HIGH_NS);
  71         return 0;
  72 }
  73
  74 static int ktd253_backlight_update_status(struct backlight_device *bl)
  75 {
  76         struct ktd253_backlight *ktd253 = bl_get_data(bl);
  77         int brightness = backlight_get_brightness(bl);
  78         u16 target_ratio;
  79         u16 current_ratio = ktd253->ratio;
  80         int ret;
  81
  82         dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness);
  83
  84         target_ratio = brightness;
  85
  86         if (target_ratio == current_ratio)
  87                 /* This is already right */
  88                 return 0;
  89
  90         if (target_ratio == 0) {
  91                 gpiod_set_value_cansleep(ktd253->gpiod, 0);
  92                 /*
  93                  * We need to keep the GPIO low for at least this long
  94                  * to actually switch the KTD253 off.
  95                  */
  96                 msleep(KTD253_T_OFF_MS);
  97                 ktd253->ratio = 0;
  98                 return 0;
  99         }
 100
 101         if (current_ratio == 0) {
 102                 ktd253_backlight_set_max_ratio(ktd253);
 103                 current_ratio = KTD253_MAX_RATIO;
 104         }
 105
 106         while (current_ratio != target_ratio) {
 107                 /*
 108                  * These GPIO operations absolutely can NOT sleep so no
 109                  * _cansleep suffixes, and no using GPIO expanders on
 110                  * slow buses for this!
 111                  */
 112                 ret = ktd253_backlight_stepdown(ktd253);
 113                 if (ret == -EAGAIN) {
 114                         /*
 115                          * Something disturbed the backlight setting code when
 116                          * running so we need to bring the PWM back to a known
 117                          * state. This shouldn't happen too much.
 118                          */
 119                         gpiod_set_value_cansleep(ktd253->gpiod, 0);
 120                         msleep(KTD253_T_OFF_MS);
 121                         ktd253_backlight_set_max_ratio(ktd253);
 122                         current_ratio = KTD253_MAX_RATIO;
 123                 } else if (current_ratio == KTD253_MIN_RATIO) {
 124                         /* After 1/32 we loop back to 32/32 */
 125                         current_ratio = KTD253_MAX_RATIO;
 126                 } else {
 127                         current_ratio--;
 128                 }
 129         }
 130         ktd253->ratio = current_ratio;
 131
 132         dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);
 133
 134         return 0;
 135 }
 136
 137 static const struct backlight_ops ktd253_backlight_ops = {
 138         .options        = BL_CORE_SUSPENDRESUME,
 139         .update_status  = ktd253_backlight_update_status,
 140 };
 141
 142 static int ktd253_backlight_probe(struct platform_device *pdev)
 143 {
 144         struct device *dev = &pdev->dev;
 145         struct backlight_device *bl;
 146         struct ktd253_backlight *ktd253;
 147         u32 max_brightness;
 148         u32 brightness;
 149         int ret;
 150
 151         ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL);
 152         if (!ktd253)
 153                 return -ENOMEM;
 154         ktd253->dev = dev;
 155
 156         ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
 157         if (ret)
 158                 max_brightness = KTD253_MAX_RATIO;
 159         if (max_brightness > KTD253_MAX_RATIO) {
 160                 /* Clamp brightness to hardware max */
 161                 dev_err(dev, "illegal max brightness specified\n");
 162                 max_brightness = KTD253_MAX_RATIO;
 163         }
 164
 165         ret = device_property_read_u32(dev, "default-brightness", &brightness);
 166         if (ret)
 167                 brightness = KTD253_DEFAULT_RATIO;
 168         if (brightness > max_brightness) {
 169                 /* Clamp default brightness to max brightness */
 170                 dev_err(dev, "default brightness exceeds max brightness\n");
 171                 brightness = max_brightness;
 172         }
 173
 174         ktd253->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
 175         if (IS_ERR(ktd253->gpiod))
 176                 return dev_err_probe(dev, PTR_ERR(ktd253->gpiod),
 177                                      "gpio line missing or invalid.\n");
 178         gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
 179         /* Bring backlight to a known off state */
 180         msleep(KTD253_T_OFF_MS);
 181
 182         bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
 183                                             &ktd253_backlight_ops, NULL);
 184         if (IS_ERR(bl)) {
 185                 dev_err(dev, "failed to register backlight\n");
 186                 return PTR_ERR(bl);
 187         }
 188         bl->props.max_brightness = max_brightness;
 189         /* When we just enable the GPIO line we set max brightness */
 190         if (brightness) {
 191                 bl->props.brightness = brightness;
 192                 bl->props.power = BACKLIGHT_POWER_ON;
 193         } else {
 194                 bl->props.brightness = 0;
 195                 bl->props.power = BACKLIGHT_POWER_OFF;
 196         }
 197
 198         ktd253->bl = bl;
 199         platform_set_drvdata(pdev, bl);
 200         backlight_update_status(bl);
 201
 202         return 0;
 203 }
 204
 205 static const struct of_device_id ktd253_backlight_of_match[] = {
 206         { .compatible = "kinetic,ktd253" },
 207         { .compatible = "kinetic,ktd259" },
 208         { /* sentinel */ }
 209 };
 210 MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
 211
 212 static struct platform_driver ktd253_backlight_driver = {
 213         .driver = {
 214                 .name = "ktd253-backlight",
 215                 .of_match_table = ktd253_backlight_of_match,
 216         },
 217         .probe          = ktd253_backlight_probe,
 218 };
 219 module_platform_driver(ktd253_backlight_driver);
 220
 221 MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
 222 MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
 223 MODULE_LICENSE("GPL");
 224 MODULE_ALIAS("platform:ktd253-backlight");