1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * The Netronix embedded controller is a microcontroller found in some |
4 | * e-book readers designed by the original design manufacturer Netronix, Inc. |
5 | * It contains RTC, battery monitoring, system power management, and PWM |
6 | * functionality. |
7 | * |
8 | * This driver implements PWM output. |
9 | * |
10 | * Copyright 2020 Jonathan Neuschäfer <j.neuschaefer@gmx.net> |
11 | * |
12 | * Limitations: |
13 | * - The get_state callback is not implemented, because the current state of |
14 | * the PWM output can't be read back from the hardware. |
15 | * - The hardware can only generate normal polarity output. |
16 | * - The period and duty cycle can't be changed together in one atomic action. |
17 | */ |
18 | |
19 | #include <linux/mfd/ntxec.h> |
20 | #include <linux/module.h> |
21 | #include <linux/platform_device.h> |
22 | #include <linux/pwm.h> |
23 | #include <linux/regmap.h> |
24 | #include <linux/types.h> |
25 | |
26 | struct ntxec_pwm { |
27 | struct ntxec *ec; |
28 | }; |
29 | |
30 | static struct ntxec_pwm *ntxec_pwm_from_chip(struct pwm_chip *chip) |
31 | { |
32 | return pwmchip_get_drvdata(chip); |
33 | } |
34 | |
35 | #define NTXEC_REG_AUTO_OFF_HI 0xa1 |
36 | #define NTXEC_REG_AUTO_OFF_LO 0xa2 |
37 | #define NTXEC_REG_ENABLE 0xa3 |
38 | #define NTXEC_REG_PERIOD_LOW 0xa4 |
39 | #define NTXEC_REG_PERIOD_HIGH 0xa5 |
40 | #define NTXEC_REG_DUTY_LOW 0xa6 |
41 | #define NTXEC_REG_DUTY_HIGH 0xa7 |
42 | |
43 | /* |
44 | * The time base used in the EC is 8MHz, or 125ns. Period and duty cycle are |
45 | * measured in this unit. |
46 | */ |
47 | #define TIME_BASE_NS 125 |
48 | |
49 | /* |
50 | * The maximum input value (in nanoseconds) is determined by the time base and |
51 | * the range of the hardware registers that hold the converted value. |
52 | * It fits into 32 bits, so we can do our calculations in 32 bits as well. |
53 | */ |
54 | #define MAX_PERIOD_NS (TIME_BASE_NS * 0xffff) |
55 | |
56 | static int ntxec_pwm_set_raw_period_and_duty_cycle(struct pwm_chip *chip, |
57 | int period, int duty) |
58 | { |
59 | struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip); |
60 | |
61 | /* |
62 | * Changes to the period and duty cycle take effect as soon as the |
63 | * corresponding low byte is written, so the hardware may be configured |
64 | * to an inconsistent state after the period is written and before the |
65 | * duty cycle is fully written. If, in such a case, the old duty cycle |
66 | * is longer than the new period, the EC may output 100% for a moment. |
67 | * |
68 | * To minimize the time between the changes to period and duty cycle |
69 | * taking effect, the writes are interleaved. |
70 | */ |
71 | |
72 | struct reg_sequence regs[] = { |
73 | { NTXEC_REG_PERIOD_HIGH, ntxec_reg8(value: period >> 8) }, |
74 | { NTXEC_REG_DUTY_HIGH, ntxec_reg8(value: duty >> 8) }, |
75 | { NTXEC_REG_PERIOD_LOW, ntxec_reg8(value: period) }, |
76 | { NTXEC_REG_DUTY_LOW, ntxec_reg8(value: duty) }, |
77 | }; |
78 | |
79 | return regmap_multi_reg_write(map: priv->ec->regmap, regs, ARRAY_SIZE(regs)); |
80 | } |
81 | |
82 | static int ntxec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm_dev, |
83 | const struct pwm_state *state) |
84 | { |
85 | struct ntxec_pwm *priv = ntxec_pwm_from_chip(chip); |
86 | unsigned int period, duty; |
87 | int res; |
88 | |
89 | if (state->polarity != PWM_POLARITY_NORMAL) |
90 | return -EINVAL; |
91 | |
92 | period = min_t(u64, state->period, MAX_PERIOD_NS); |
93 | duty = min_t(u64, state->duty_cycle, period); |
94 | |
95 | period /= TIME_BASE_NS; |
96 | duty /= TIME_BASE_NS; |
97 | |
98 | /* |
99 | * Writing a duty cycle of zero puts the device into a state where |
100 | * writing a higher duty cycle doesn't result in the brightness that it |
101 | * usually results in. This can be fixed by cycling the ENABLE register. |
102 | * |
103 | * As a workaround, write ENABLE=0 when the duty cycle is zero. |
104 | * The case that something has previously set the duty cycle to zero |
105 | * but ENABLE=1, is not handled. |
106 | */ |
107 | if (state->enabled && duty != 0) { |
108 | res = ntxec_pwm_set_raw_period_and_duty_cycle(chip, period, duty); |
109 | if (res) |
110 | return res; |
111 | |
112 | res = regmap_write(map: priv->ec->regmap, NTXEC_REG_ENABLE, val: ntxec_reg8(value: 1)); |
113 | if (res) |
114 | return res; |
115 | |
116 | /* Disable the auto-off timer */ |
117 | res = regmap_write(map: priv->ec->regmap, NTXEC_REG_AUTO_OFF_HI, val: ntxec_reg8(value: 0xff)); |
118 | if (res) |
119 | return res; |
120 | |
121 | return regmap_write(map: priv->ec->regmap, NTXEC_REG_AUTO_OFF_LO, val: ntxec_reg8(value: 0xff)); |
122 | } else { |
123 | return regmap_write(map: priv->ec->regmap, NTXEC_REG_ENABLE, val: ntxec_reg8(value: 0)); |
124 | } |
125 | } |
126 | |
127 | static const struct pwm_ops ntxec_pwm_ops = { |
128 | .apply = ntxec_pwm_apply, |
129 | /* |
130 | * No .get_state callback, because the current state cannot be read |
131 | * back from the hardware. |
132 | */ |
133 | }; |
134 | |
135 | static int ntxec_pwm_probe(struct platform_device *pdev) |
136 | { |
137 | struct ntxec *ec = dev_get_drvdata(dev: pdev->dev.parent); |
138 | struct ntxec_pwm *priv; |
139 | struct pwm_chip *chip; |
140 | |
141 | device_set_of_node_from_dev(dev: &pdev->dev, dev2: pdev->dev.parent); |
142 | |
143 | chip = devm_pwmchip_alloc(parent: &pdev->dev, npwm: 1, sizeof_priv: sizeof(*priv)); |
144 | if (IS_ERR(ptr: chip)) |
145 | return PTR_ERR(ptr: chip); |
146 | priv = ntxec_pwm_from_chip(chip); |
147 | |
148 | priv->ec = ec; |
149 | chip->ops = &ntxec_pwm_ops; |
150 | |
151 | return devm_pwmchip_add(&pdev->dev, chip); |
152 | } |
153 | |
154 | static struct platform_driver ntxec_pwm_driver = { |
155 | .driver = { |
156 | .name = "ntxec-pwm" , |
157 | }, |
158 | .probe = ntxec_pwm_probe, |
159 | }; |
160 | module_platform_driver(ntxec_pwm_driver); |
161 | |
162 | MODULE_AUTHOR("Jonathan Neuschäfer <j.neuschaefer@gmx.net>" ); |
163 | MODULE_DESCRIPTION("PWM driver for Netronix EC" ); |
164 | MODULE_LICENSE("GPL" ); |
165 | MODULE_ALIAS("platform:ntxec-pwm" ); |
166 | |