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/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_CRIT_NS 100000 /* 100 us, now it doesn't look good */
29 #define KTD253_T_OFF_MS 3
30
31 struct ktd253_backlight {
32 struct device *dev;
33 struct backlight_device *bl;
34 struct gpio_desc *gpiod;
35 u16 ratio;
36 };
37
ktd253_backlight_set_max_ratio(struct ktd253_backlight * ktd253)38 static void ktd253_backlight_set_max_ratio(struct ktd253_backlight *ktd253)
39 {
40 gpiod_set_value_cansleep(ktd253->gpiod, 1);
41 ndelay(KTD253_T_HIGH_NS);
42 /* We always fall back to this when we power on */
43 }
44
ktd253_backlight_stepdown(struct ktd253_backlight * ktd253)45 static int ktd253_backlight_stepdown(struct ktd253_backlight *ktd253)
46 {
47 /*
48 * These GPIO operations absolutely can NOT sleep so no _cansleep
49 * suffixes, and no using GPIO expanders on slow buses for this!
50 *
51 * The maximum number of cycles of the loop is 32 so the time taken
52 * should nominally be:
53 * (T_LOW_NS + T_HIGH_NS + loop_time) * 32
54 *
55 * Architectures do not always support ndelay() and we will get a few us
56 * instead. If we get to a critical time limit an interrupt has likely
57 * occured in the low part of the loop and we need to restart from the
58 * top so we have the backlight in a known state.
59 */
60 u64 ns;
61
62 ns = ktime_get_ns();
63 gpiod_set_value(ktd253->gpiod, 0);
64 ndelay(KTD253_T_LOW_NS);
65 gpiod_set_value(ktd253->gpiod, 1);
66 ns = ktime_get_ns() - ns;
67 if (ns >= KTD253_T_OFF_CRIT_NS) {
68 dev_err(ktd253->dev, "PCM on backlight took too long (%llu ns)\n", ns);
69 return -EAGAIN;
70 }
71 ndelay(KTD253_T_HIGH_NS);
72 return 0;
73 }
74
ktd253_backlight_update_status(struct backlight_device * bl)75 static int ktd253_backlight_update_status(struct backlight_device *bl)
76 {
77 struct ktd253_backlight *ktd253 = bl_get_data(bl);
78 int brightness = backlight_get_brightness(bl);
79 u16 target_ratio;
80 u16 current_ratio = ktd253->ratio;
81 int ret;
82
83 dev_dbg(ktd253->dev, "new brightness/ratio: %d/32\n", brightness);
84
85 target_ratio = brightness;
86
87 if (target_ratio == current_ratio)
88 /* This is already right */
89 return 0;
90
91 if (target_ratio == 0) {
92 gpiod_set_value_cansleep(ktd253->gpiod, 0);
93 /*
94 * We need to keep the GPIO low for at least this long
95 * to actually switch the KTD253 off.
96 */
97 msleep(KTD253_T_OFF_MS);
98 ktd253->ratio = 0;
99 return 0;
100 }
101
102 if (current_ratio == 0) {
103 ktd253_backlight_set_max_ratio(ktd253);
104 current_ratio = KTD253_MAX_RATIO;
105 }
106
107 while (current_ratio != target_ratio) {
108 /*
109 * These GPIO operations absolutely can NOT sleep so no
110 * _cansleep suffixes, and no using GPIO expanders on
111 * slow buses for this!
112 */
113 ret = ktd253_backlight_stepdown(ktd253);
114 if (ret == -EAGAIN) {
115 /*
116 * Something disturbed the backlight setting code when
117 * running so we need to bring the PWM back to a known
118 * state. This shouldn't happen too much.
119 */
120 gpiod_set_value_cansleep(ktd253->gpiod, 0);
121 msleep(KTD253_T_OFF_MS);
122 ktd253_backlight_set_max_ratio(ktd253);
123 current_ratio = KTD253_MAX_RATIO;
124 } else if (current_ratio == KTD253_MIN_RATIO) {
125 /* After 1/32 we loop back to 32/32 */
126 current_ratio = KTD253_MAX_RATIO;
127 } else {
128 current_ratio--;
129 }
130 }
131 ktd253->ratio = current_ratio;
132
133 dev_dbg(ktd253->dev, "new ratio set to %d/32\n", target_ratio);
134
135 return 0;
136 }
137
138 static const struct backlight_ops ktd253_backlight_ops = {
139 .options = BL_CORE_SUSPENDRESUME,
140 .update_status = ktd253_backlight_update_status,
141 };
142
ktd253_backlight_probe(struct platform_device * pdev)143 static int ktd253_backlight_probe(struct platform_device *pdev)
144 {
145 struct device *dev = &pdev->dev;
146 struct backlight_device *bl;
147 struct ktd253_backlight *ktd253;
148 u32 max_brightness;
149 u32 brightness;
150 int ret;
151
152 ktd253 = devm_kzalloc(dev, sizeof(*ktd253), GFP_KERNEL);
153 if (!ktd253)
154 return -ENOMEM;
155 ktd253->dev = dev;
156
157 ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
158 if (ret)
159 max_brightness = KTD253_MAX_RATIO;
160 if (max_brightness > KTD253_MAX_RATIO) {
161 /* Clamp brightness to hardware max */
162 dev_err(dev, "illegal max brightness specified\n");
163 max_brightness = KTD253_MAX_RATIO;
164 }
165
166 ret = device_property_read_u32(dev, "default-brightness", &brightness);
167 if (ret)
168 brightness = KTD253_DEFAULT_RATIO;
169 if (brightness > max_brightness) {
170 /* Clamp default brightness to max brightness */
171 dev_err(dev, "default brightness exceeds max brightness\n");
172 brightness = max_brightness;
173 }
174
175 ktd253->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
176 if (IS_ERR(ktd253->gpiod))
177 return dev_err_probe(dev, PTR_ERR(ktd253->gpiod),
178 "gpio line missing or invalid.\n");
179 gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
180 /* Bring backlight to a known off state */
181 msleep(KTD253_T_OFF_MS);
182
183 bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
184 &ktd253_backlight_ops, NULL);
185 if (IS_ERR(bl)) {
186 dev_err(dev, "failed to register backlight\n");
187 return PTR_ERR(bl);
188 }
189 bl->props.max_brightness = max_brightness;
190 /* When we just enable the GPIO line we set max brightness */
191 if (brightness) {
192 bl->props.brightness = brightness;
193 bl->props.power = FB_BLANK_UNBLANK;
194 } else {
195 bl->props.brightness = 0;
196 bl->props.power = FB_BLANK_POWERDOWN;
197 }
198
199 ktd253->bl = bl;
200 platform_set_drvdata(pdev, bl);
201 backlight_update_status(bl);
202
203 return 0;
204 }
205
206 static const struct of_device_id ktd253_backlight_of_match[] = {
207 { .compatible = "kinetic,ktd253" },
208 { .compatible = "kinetic,ktd259" },
209 { /* sentinel */ }
210 };
211 MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
212
213 static struct platform_driver ktd253_backlight_driver = {
214 .driver = {
215 .name = "ktd253-backlight",
216 .of_match_table = ktd253_backlight_of_match,
217 },
218 .probe = ktd253_backlight_probe,
219 };
220 module_platform_driver(ktd253_backlight_driver);
221
222 MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
223 MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
224 MODULE_LICENSE("GPL");
225 MODULE_ALIAS("platform:ktd253-backlight");
226
