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_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 	ktd253->gpiod = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
141 	if (IS_ERR(ktd253->gpiod)) {
142 		ret = PTR_ERR(ktd253->gpiod);
143 		if (ret != -EPROBE_DEFER)
144 			dev_err(dev, "gpio line missing or invalid.\n");
145 		return ret;
146 	}
147 	gpiod_set_consumer_name(ktd253->gpiod, dev_name(dev));
148 	/* Bring backlight to a known off state */
149 	msleep(KTD253_T_OFF_MS);
150 
151 	bl = devm_backlight_device_register(dev, dev_name(dev), dev, ktd253,
152 					    &ktd253_backlight_ops, NULL);
153 	if (IS_ERR(bl)) {
154 		dev_err(dev, "failed to register backlight\n");
155 		return PTR_ERR(bl);
156 	}
157 	bl->props.max_brightness = max_brightness;
158 	/* When we just enable the GPIO line we set max brightness */
159 	if (brightness) {
160 		bl->props.brightness = brightness;
161 		bl->props.power = FB_BLANK_UNBLANK;
162 	} else {
163 		bl->props.brightness = 0;
164 		bl->props.power = FB_BLANK_POWERDOWN;
165 	}
166 
167 	ktd253->bl = bl;
168 	platform_set_drvdata(pdev, bl);
169 	backlight_update_status(bl);
170 
171 	return 0;
172 }
173 
174 static const struct of_device_id ktd253_backlight_of_match[] = {
175 	{ .compatible = "kinetic,ktd253" },
176 	{ .compatible = "kinetic,ktd259" },
177 	{ /* sentinel */ }
178 };
179 MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
180 
181 static struct platform_driver ktd253_backlight_driver = {
182 	.driver = {
183 		.name = "ktd253-backlight",
184 		.of_match_table = ktd253_backlight_of_match,
185 	},
186 	.probe		= ktd253_backlight_probe,
187 };
188 module_platform_driver(ktd253_backlight_driver);
189 
190 MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
191 MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
192 MODULE_LICENSE("GPL");
193 MODULE_ALIAS("platform:ktd253-backlight");
194