1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * sl28cpld PWM driver
4 *
5 * Copyright (c) 2020 Michael Walle <michael@walle.cc>
6 *
7 * There is no public datasheet available for this PWM core. But it is easy
8 * enough to be briefly explained. It consists of one 8-bit counter. The PWM
9 * supports four distinct frequencies by selecting when to reset the counter.
10 * With the prescaler setting you can select which bit of the counter is used
11 * to reset it. This implies that the higher the frequency the less remaining
12 * bits are available for the actual counter.
13 *
14 * Let cnt[7:0] be the counter, clocked at 32kHz:
15 * +-----------+--------+--------------+-----------+---------------+
16 * | prescaler | reset | counter bits | frequency | period length |
17 * +-----------+--------+--------------+-----------+---------------+
18 * | 0 | cnt[7] | cnt[6:0] | 250 Hz | 4000000 ns |
19 * | 1 | cnt[6] | cnt[5:0] | 500 Hz | 2000000 ns |
20 * | 2 | cnt[5] | cnt[4:0] | 1 kHz | 1000000 ns |
21 * | 3 | cnt[4] | cnt[3:0] | 2 kHz | 500000 ns |
22 * +-----------+--------+--------------+-----------+---------------+
23 *
24 * Limitations:
25 * - The hardware cannot generate a 100% duty cycle if the prescaler is 0.
26 * - The hardware cannot atomically set the prescaler and the counter value,
27 * which might lead to glitches and inconsistent states if a write fails.
28 * - The counter is not reset if you switch the prescaler which leads
29 * to glitches, too.
30 * - The duty cycle will switch immediately and not after a complete cycle.
31 * - Depending on the actual implementation, disabling the PWM might have
32 * side effects. For example, if the output pin is shared with a GPIO pin
33 * it will automatically switch back to GPIO mode.
34 */
35
36 #include <linux/bitfield.h>
37 #include <linux/kernel.h>
38 #include <linux/mod_devicetable.h>
39 #include <linux/module.h>
40 #include <linux/platform_device.h>
41 #include <linux/pwm.h>
42 #include <linux/regmap.h>
43
44 /*
45 * PWM timer block registers.
46 */
47 #define SL28CPLD_PWM_CTRL 0x00
48 #define SL28CPLD_PWM_CTRL_ENABLE BIT(7)
49 #define SL28CPLD_PWM_CTRL_PRESCALER_MASK GENMASK(1, 0)
50 #define SL28CPLD_PWM_CYCLE 0x01
51 #define SL28CPLD_PWM_CYCLE_MAX GENMASK(6, 0)
52
53 #define SL28CPLD_PWM_CLK 32000 /* 32 kHz */
54 #define SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler) (1 << (7 - (prescaler)))
55 #define SL28CPLD_PWM_PERIOD(prescaler) \
56 (NSEC_PER_SEC / SL28CPLD_PWM_CLK * SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler))
57
58 /*
59 * We calculate the duty cycle like this:
60 * duty_cycle_ns = pwm_cycle_reg * max_period_ns / max_duty_cycle
61 *
62 * With
63 * max_period_ns = 1 << (7 - prescaler) / SL28CPLD_PWM_CLK * NSEC_PER_SEC
64 * max_duty_cycle = 1 << (7 - prescaler)
65 * this then simplifies to:
66 * duty_cycle_ns = pwm_cycle_reg / SL28CPLD_PWM_CLK * NSEC_PER_SEC
67 * = NSEC_PER_SEC / SL28CPLD_PWM_CLK * pwm_cycle_reg
68 *
69 * NSEC_PER_SEC is a multiple of SL28CPLD_PWM_CLK, therefore we're not losing
70 * precision by doing the divison first.
71 */
72 #define SL28CPLD_PWM_TO_DUTY_CYCLE(reg) \
73 (NSEC_PER_SEC / SL28CPLD_PWM_CLK * (reg))
74 #define SL28CPLD_PWM_FROM_DUTY_CYCLE(duty_cycle) \
75 (DIV_ROUND_DOWN_ULL((duty_cycle), NSEC_PER_SEC / SL28CPLD_PWM_CLK))
76
77 #define sl28cpld_pwm_read(priv, reg, val) \
78 regmap_read((priv)->regmap, (priv)->offset + (reg), (val))
79 #define sl28cpld_pwm_write(priv, reg, val) \
80 regmap_write((priv)->regmap, (priv)->offset + (reg), (val))
81
82 struct sl28cpld_pwm {
83 struct pwm_chip pwm_chip;
84 struct regmap *regmap;
85 u32 offset;
86 };
87 #define sl28cpld_pwm_from_chip(_chip) \
88 container_of(_chip, struct sl28cpld_pwm, pwm_chip)
89
sl28cpld_pwm_get_state(struct pwm_chip * chip,struct pwm_device * pwm,struct pwm_state * state)90 static void sl28cpld_pwm_get_state(struct pwm_chip *chip,
91 struct pwm_device *pwm,
92 struct pwm_state *state)
93 {
94 struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
95 unsigned int reg;
96 int prescaler;
97
98 sl28cpld_pwm_read(priv, SL28CPLD_PWM_CTRL, ®);
99
100 state->enabled = reg & SL28CPLD_PWM_CTRL_ENABLE;
101
102 prescaler = FIELD_GET(SL28CPLD_PWM_CTRL_PRESCALER_MASK, reg);
103 state->period = SL28CPLD_PWM_PERIOD(prescaler);
104
105 sl28cpld_pwm_read(priv, SL28CPLD_PWM_CYCLE, ®);
106 state->duty_cycle = SL28CPLD_PWM_TO_DUTY_CYCLE(reg);
107 state->polarity = PWM_POLARITY_NORMAL;
108
109 /*
110 * Sanitize values for the PWM core. Depending on the prescaler it
111 * might happen that we calculate a duty_cycle greater than the actual
112 * period. This might happen if someone (e.g. the bootloader) sets an
113 * invalid combination of values. The behavior of the hardware is
114 * undefined in this case. But we need to report sane values back to
115 * the PWM core.
116 */
117 state->duty_cycle = min(state->duty_cycle, state->period);
118 }
119
sl28cpld_pwm_apply(struct pwm_chip * chip,struct pwm_device * pwm,const struct pwm_state * state)120 static int sl28cpld_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
121 const struct pwm_state *state)
122 {
123 struct sl28cpld_pwm *priv = sl28cpld_pwm_from_chip(chip);
124 unsigned int cycle, prescaler;
125 bool write_duty_cycle_first;
126 int ret;
127 u8 ctrl;
128
129 /* Polarity inversion is not supported */
130 if (state->polarity != PWM_POLARITY_NORMAL)
131 return -EINVAL;
132
133 /*
134 * Calculate the prescaler. Pick the biggest period that isn't
135 * bigger than the requested period.
136 */
137 prescaler = DIV_ROUND_UP_ULL(SL28CPLD_PWM_PERIOD(0), state->period);
138 prescaler = order_base_2(prescaler);
139
140 if (prescaler > field_max(SL28CPLD_PWM_CTRL_PRESCALER_MASK))
141 return -ERANGE;
142
143 ctrl = FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, prescaler);
144 if (state->enabled)
145 ctrl |= SL28CPLD_PWM_CTRL_ENABLE;
146
147 cycle = SL28CPLD_PWM_FROM_DUTY_CYCLE(state->duty_cycle);
148 cycle = min_t(unsigned int, cycle, SL28CPLD_PWM_MAX_DUTY_CYCLE(prescaler));
149
150 /*
151 * Work around the hardware limitation. See also above. Trap 100% duty
152 * cycle if the prescaler is 0. Set prescaler to 1 instead. We don't
153 * care about the frequency because its "all-one" in either case.
154 *
155 * We don't need to check the actual prescaler setting, because only
156 * if the prescaler is 0 we can have this particular value.
157 */
158 if (cycle == SL28CPLD_PWM_MAX_DUTY_CYCLE(0)) {
159 ctrl &= ~SL28CPLD_PWM_CTRL_PRESCALER_MASK;
160 ctrl |= FIELD_PREP(SL28CPLD_PWM_CTRL_PRESCALER_MASK, 1);
161 cycle = SL28CPLD_PWM_MAX_DUTY_CYCLE(1);
162 }
163
164 /*
165 * To avoid glitches when we switch the prescaler, we have to make sure
166 * we have a valid duty cycle for the new mode.
167 *
168 * Take the current prescaler (or the current period length) into
169 * account to decide whether we have to write the duty cycle or the new
170 * prescaler first. If the period length is decreasing we have to
171 * write the duty cycle first.
172 */
173 write_duty_cycle_first = pwm->state.period > state->period;
174
175 if (write_duty_cycle_first) {
176 ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
177 if (ret)
178 return ret;
179 }
180
181 ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CTRL, ctrl);
182 if (ret)
183 return ret;
184
185 if (!write_duty_cycle_first) {
186 ret = sl28cpld_pwm_write(priv, SL28CPLD_PWM_CYCLE, cycle);
187 if (ret)
188 return ret;
189 }
190
191 return 0;
192 }
193
194 static const struct pwm_ops sl28cpld_pwm_ops = {
195 .apply = sl28cpld_pwm_apply,
196 .get_state = sl28cpld_pwm_get_state,
197 .owner = THIS_MODULE,
198 };
199
sl28cpld_pwm_probe(struct platform_device * pdev)200 static int sl28cpld_pwm_probe(struct platform_device *pdev)
201 {
202 struct sl28cpld_pwm *priv;
203 struct pwm_chip *chip;
204 int ret;
205
206 if (!pdev->dev.parent) {
207 dev_err(&pdev->dev, "no parent device\n");
208 return -ENODEV;
209 }
210
211 priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
212 if (!priv)
213 return -ENOMEM;
214
215 priv->regmap = dev_get_regmap(pdev->dev.parent, NULL);
216 if (!priv->regmap) {
217 dev_err(&pdev->dev, "could not get parent regmap\n");
218 return -ENODEV;
219 }
220
221 ret = device_property_read_u32(&pdev->dev, "reg", &priv->offset);
222 if (ret) {
223 dev_err(&pdev->dev, "no 'reg' property found (%pe)\n",
224 ERR_PTR(ret));
225 return -EINVAL;
226 }
227
228 /* Initialize the pwm_chip structure */
229 chip = &priv->pwm_chip;
230 chip->dev = &pdev->dev;
231 chip->ops = &sl28cpld_pwm_ops;
232 chip->npwm = 1;
233
234 platform_set_drvdata(pdev, priv);
235
236 ret = pwmchip_add(&priv->pwm_chip);
237 if (ret) {
238 dev_err(&pdev->dev, "failed to add PWM chip (%pe)",
239 ERR_PTR(ret));
240 return ret;
241 }
242
243 return 0;
244 }
245
sl28cpld_pwm_remove(struct platform_device * pdev)246 static int sl28cpld_pwm_remove(struct platform_device *pdev)
247 {
248 struct sl28cpld_pwm *priv = platform_get_drvdata(pdev);
249
250 return pwmchip_remove(&priv->pwm_chip);
251 }
252
253 static const struct of_device_id sl28cpld_pwm_of_match[] = {
254 { .compatible = "kontron,sl28cpld-pwm" },
255 {}
256 };
257 MODULE_DEVICE_TABLE(of, sl28cpld_pwm_of_match);
258
259 static struct platform_driver sl28cpld_pwm_driver = {
260 .probe = sl28cpld_pwm_probe,
261 .remove = sl28cpld_pwm_remove,
262 .driver = {
263 .name = "sl28cpld-pwm",
264 .of_match_table = sl28cpld_pwm_of_match,
265 },
266 };
267 module_platform_driver(sl28cpld_pwm_driver);
268
269 MODULE_DESCRIPTION("sl28cpld PWM Driver");
270 MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
271 MODULE_LICENSE("GPL");
272