tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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
30struct ktd253_backlight {
31 struct device *dev;
32 struct backlight_device *bl;
33 struct gpio_desc *gpiod;
34 u16 ratio;
35};
36
37static 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
103static const struct backlight_ops ktd253_backlight_ops = {
104 .options = BL_CORE_SUSPENDRESUME,
105 .update_status = ktd253_backlight_update_status,
106};
107
108static 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
174static const struct of_device_id ktd253_backlight_of_match[] = {
175 { .compatible = "kinetic,ktd253" },
176 { .compatible = "kinetic,ktd259" },
177 { /* sentinel */ }
178};
179MODULE_DEVICE_TABLE(of, ktd253_backlight_of_match);
180
181static 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};
188module_platform_driver(ktd253_backlight_driver);
189
190MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
191MODULE_DESCRIPTION("Kinetic KTD253 Backlight Driver");
192MODULE_LICENSE("GPL");
193MODULE_ALIAS("platform:ktd253-backlight");