1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * Azoteq IQS620A PWM Generator
4  *
5  * Copyright (C) 2019 Jeff LaBundy <jeff@labundy.com>
6  *
7  * Limitations:
8  * - The period is fixed to 1 ms and is generated continuously despite changes
9  *   to the duty cycle or enable/disable state.
10  * - Changes to the duty cycle or enable/disable state take effect immediately
11  *   and may result in a glitch during the period in which the change is made.
12  * - The device cannot generate a 0% duty cycle. For duty cycles below 1 / 256
13  *   ms, the output is disabled and relies upon an external pull-down resistor
14  *   to hold the GPIO3/LTX pin low.
15  */
16 
17 #include <linux/device.h>
18 #include <linux/kernel.h>
19 #include <linux/mfd/iqs62x.h>
20 #include <linux/module.h>
21 #include <linux/mutex.h>
22 #include <linux/notifier.h>
23 #include <linux/platform_device.h>
24 #include <linux/pwm.h>
25 #include <linux/regmap.h>
26 #include <linux/slab.h>
27 
28 #define IQS620_PWR_SETTINGS			0xd2
29 #define IQS620_PWR_SETTINGS_PWM_OUT		BIT(7)
30 
31 #define IQS620_PWM_DUTY_CYCLE			0xd8
32 
33 #define IQS620_PWM_PERIOD_NS			1000000
34 
35 struct iqs620_pwm_private {
36 	struct iqs62x_core *iqs62x;
37 	struct pwm_chip chip;
38 	struct notifier_block notifier;
39 	struct mutex lock;
40 	unsigned int duty_scale;
41 };
42 
iqs620_pwm_init(struct iqs620_pwm_private * iqs620_pwm,unsigned int duty_scale)43 static int iqs620_pwm_init(struct iqs620_pwm_private *iqs620_pwm,
44 			   unsigned int duty_scale)
45 {
46 	struct iqs62x_core *iqs62x = iqs620_pwm->iqs62x;
47 	int ret;
48 
49 	if (!duty_scale)
50 		return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
51 					  IQS620_PWR_SETTINGS_PWM_OUT, 0);
52 
53 	ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
54 			   duty_scale - 1);
55 	if (ret)
56 		return ret;
57 
58 	return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
59 				  IQS620_PWR_SETTINGS_PWM_OUT, 0xff);
60 }
61 
iqs620_pwm_apply(struct pwm_chip * chip,struct pwm_device * pwm,const struct pwm_state * state)62 static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
63 			    const struct pwm_state *state)
64 {
65 	struct iqs620_pwm_private *iqs620_pwm;
66 	unsigned int duty_cycle;
67 	unsigned int duty_scale;
68 	int ret;
69 
70 	if (state->polarity != PWM_POLARITY_NORMAL)
71 		return -EINVAL;
72 
73 	if (state->period < IQS620_PWM_PERIOD_NS)
74 		return -EINVAL;
75 
76 	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
77 
78 	/*
79 	 * The duty cycle generated by the device is calculated as follows:
80 	 *
81 	 * duty_cycle = (IQS620_PWM_DUTY_CYCLE + 1) / 256 * 1 ms
82 	 *
83 	 * ...where IQS620_PWM_DUTY_CYCLE is a register value between 0 and 255
84 	 * (inclusive). Therefore the lowest duty cycle the device can generate
85 	 * while the output is enabled is 1 / 256 ms.
86 	 *
87 	 * For lower duty cycles (e.g. 0), the PWM output is simply disabled to
88 	 * allow an external pull-down resistor to hold the GPIO3/LTX pin low.
89 	 */
90 	duty_cycle = min_t(u64, state->duty_cycle, IQS620_PWM_PERIOD_NS);
91 	duty_scale = duty_cycle * 256 / IQS620_PWM_PERIOD_NS;
92 
93 	if (!state->enabled)
94 		duty_scale = 0;
95 
96 	mutex_lock(&iqs620_pwm->lock);
97 
98 	ret = iqs620_pwm_init(iqs620_pwm, duty_scale);
99 	if (!ret)
100 		iqs620_pwm->duty_scale = duty_scale;
101 
102 	mutex_unlock(&iqs620_pwm->lock);
103 
104 	return ret;
105 }
106 
iqs620_pwm_get_state(struct pwm_chip * chip,struct pwm_device * pwm,struct pwm_state * state)107 static void iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
108 				 struct pwm_state *state)
109 {
110 	struct iqs620_pwm_private *iqs620_pwm;
111 
112 	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
113 
114 	mutex_lock(&iqs620_pwm->lock);
115 
116 	/*
117 	 * Since the device cannot generate a 0% duty cycle, requests to do so
118 	 * cause subsequent calls to iqs620_pwm_get_state to report the output
119 	 * as disabled. This is not ideal, but is the best compromise based on
120 	 * the capabilities of the device.
121 	 */
122 	state->enabled = iqs620_pwm->duty_scale > 0;
123 	state->duty_cycle = DIV_ROUND_UP(iqs620_pwm->duty_scale *
124 					 IQS620_PWM_PERIOD_NS, 256);
125 
126 	mutex_unlock(&iqs620_pwm->lock);
127 
128 	state->period = IQS620_PWM_PERIOD_NS;
129 }
130 
iqs620_pwm_notifier(struct notifier_block * notifier,unsigned long event_flags,void * context)131 static int iqs620_pwm_notifier(struct notifier_block *notifier,
132 			       unsigned long event_flags, void *context)
133 {
134 	struct iqs620_pwm_private *iqs620_pwm;
135 	int ret;
136 
137 	if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
138 		return NOTIFY_DONE;
139 
140 	iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
141 				  notifier);
142 
143 	mutex_lock(&iqs620_pwm->lock);
144 
145 	/*
146 	 * The parent MFD driver already prints an error message in the event
147 	 * of a device reset, so nothing else is printed here unless there is
148 	 * an additional failure.
149 	 */
150 	ret = iqs620_pwm_init(iqs620_pwm, iqs620_pwm->duty_scale);
151 
152 	mutex_unlock(&iqs620_pwm->lock);
153 
154 	if (ret) {
155 		dev_err(iqs620_pwm->chip.dev,
156 			"Failed to re-initialize device: %d\n", ret);
157 		return NOTIFY_BAD;
158 	}
159 
160 	return NOTIFY_OK;
161 }
162 
163 static const struct pwm_ops iqs620_pwm_ops = {
164 	.apply = iqs620_pwm_apply,
165 	.get_state = iqs620_pwm_get_state,
166 	.owner = THIS_MODULE,
167 };
168 
iqs620_pwm_notifier_unregister(void * context)169 static void iqs620_pwm_notifier_unregister(void *context)
170 {
171 	struct iqs620_pwm_private *iqs620_pwm = context;
172 	int ret;
173 
174 	ret = blocking_notifier_chain_unregister(&iqs620_pwm->iqs62x->nh,
175 						 &iqs620_pwm->notifier);
176 	if (ret)
177 		dev_err(iqs620_pwm->chip.dev,
178 			"Failed to unregister notifier: %d\n", ret);
179 }
180 
iqs620_pwm_probe(struct platform_device * pdev)181 static int iqs620_pwm_probe(struct platform_device *pdev)
182 {
183 	struct iqs62x_core *iqs62x = dev_get_drvdata(pdev->dev.parent);
184 	struct iqs620_pwm_private *iqs620_pwm;
185 	unsigned int val;
186 	int ret;
187 
188 	iqs620_pwm = devm_kzalloc(&pdev->dev, sizeof(*iqs620_pwm), GFP_KERNEL);
189 	if (!iqs620_pwm)
190 		return -ENOMEM;
191 
192 	iqs620_pwm->iqs62x = iqs62x;
193 
194 	ret = regmap_read(iqs62x->regmap, IQS620_PWR_SETTINGS, &val);
195 	if (ret)
196 		return ret;
197 
198 	if (val & IQS620_PWR_SETTINGS_PWM_OUT) {
199 		ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
200 		if (ret)
201 			return ret;
202 
203 		iqs620_pwm->duty_scale = val + 1;
204 	}
205 
206 	iqs620_pwm->chip.dev = &pdev->dev;
207 	iqs620_pwm->chip.ops = &iqs620_pwm_ops;
208 	iqs620_pwm->chip.npwm = 1;
209 
210 	mutex_init(&iqs620_pwm->lock);
211 
212 	iqs620_pwm->notifier.notifier_call = iqs620_pwm_notifier;
213 	ret = blocking_notifier_chain_register(&iqs620_pwm->iqs62x->nh,
214 					       &iqs620_pwm->notifier);
215 	if (ret) {
216 		dev_err(&pdev->dev, "Failed to register notifier: %d\n", ret);
217 		return ret;
218 	}
219 
220 	ret = devm_add_action_or_reset(&pdev->dev,
221 				       iqs620_pwm_notifier_unregister,
222 				       iqs620_pwm);
223 	if (ret)
224 		return ret;
225 
226 	ret = devm_pwmchip_add(&pdev->dev, &iqs620_pwm->chip);
227 	if (ret)
228 		dev_err(&pdev->dev, "Failed to add device: %d\n", ret);
229 
230 	return ret;
231 }
232 
233 static struct platform_driver iqs620_pwm_platform_driver = {
234 	.driver = {
235 		.name = "iqs620a-pwm",
236 	},
237 	.probe = iqs620_pwm_probe,
238 };
239 module_platform_driver(iqs620_pwm_platform_driver);
240 
241 MODULE_AUTHOR("Jeff LaBundy <jeff@labundy.com>");
242 MODULE_DESCRIPTION("Azoteq IQS620A PWM Generator");
243 MODULE_LICENSE("GPL");
244 MODULE_ALIAS("platform:iqs620a-pwm");
245