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 
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 
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 
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 
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