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
ktd253_backlight_set_max_ratio(struct ktd253_backlight * ktd253)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
ktd253_backlight_stepdown(struct ktd253_backlight * ktd253)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
ktd253_backlight_update_status(struct backlight_device * bl)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
ktd253_backlight_probe(struct platform_device * pdev)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");
225