1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * corePWM driver for Microchip "soft" FPGA IP cores.
4  *
5  * Copyright (c) 2021-2023 Microchip Corporation. All rights reserved.
6  * Author: Conor Dooley <conor.dooley@microchip.com>
7  * Documentation:
8  * https://www.microsemi.com/document-portal/doc_download/1245275-corepwm-hb
9  *
10  * Limitations:
11  * - If the IP block is configured without "shadow registers", all register
12  *   writes will take effect immediately, causing glitches on the output.
13  *   If shadow registers *are* enabled, setting the "SYNC_UPDATE" register
14  *   notifies the core that it needs to update the registers defining the
15  *   waveform from the contents of the "shadow registers". Otherwise, changes
16  *   will take effective immediately, even for those channels.
17  *   As setting the period/duty cycle takes 4 register writes, there is a window
18  *   in which this races against the start of a new period.
19  * - The IP block has no concept of a duty cycle, only rising/falling edges of
20  *   the waveform. Unfortunately, if the rising & falling edges registers have
21  *   the same value written to them the IP block will do whichever of a rising
22  *   or a falling edge is possible. I.E. a 50% waveform at twice the requested
23  *   period. Therefore to get a 0% waveform, the output is set the max high/low
24  *   time depending on polarity.
25  *   If the duty cycle is 0%, and the requested period is less than the
26  *   available period resolution, this will manifest as a ~100% waveform (with
27  *   some output glitches) rather than 50%.
28  * - The PWM period is set for the whole IP block not per channel. The driver
29  *   will only change the period if no other PWM output is enabled.
30  */
31 
32 #include <linux/clk.h>
33 #include <linux/delay.h>
34 #include <linux/err.h>
35 #include <linux/io.h>
36 #include <linux/ktime.h>
37 #include <linux/math.h>
38 #include <linux/module.h>
39 #include <linux/mutex.h>
40 #include <linux/of.h>
41 #include <linux/platform_device.h>
42 #include <linux/pwm.h>
43 
44 #define MCHPCOREPWM_PRESCALE_MAX	0xff
45 #define MCHPCOREPWM_PERIOD_STEPS_MAX	0xfe
46 #define MCHPCOREPWM_PERIOD_MAX		0xff00
47 
48 #define MCHPCOREPWM_PRESCALE	0x00
49 #define MCHPCOREPWM_PERIOD	0x04
50 #define MCHPCOREPWM_EN(i)	(0x08 + 0x04 * (i)) /* 0x08, 0x0c */
51 #define MCHPCOREPWM_POSEDGE(i)	(0x10 + 0x08 * (i)) /* 0x10, 0x18, ..., 0x88 */
52 #define MCHPCOREPWM_NEGEDGE(i)	(0x14 + 0x08 * (i)) /* 0x14, 0x1c, ..., 0x8c */
53 #define MCHPCOREPWM_SYNC_UPD	0xe4
54 #define MCHPCOREPWM_TIMEOUT_MS	100u
55 
56 struct mchp_core_pwm_chip {
57 	struct pwm_chip chip;
58 	struct clk *clk;
59 	void __iomem *base;
60 	struct mutex lock; /* protects the shared period */
61 	ktime_t update_timestamp;
62 	u32 sync_update_mask;
63 	u16 channel_enabled;
64 };
65 
66 static inline struct mchp_core_pwm_chip *to_mchp_core_pwm(struct pwm_chip *chip)
67 {
68 	return container_of(chip, struct mchp_core_pwm_chip, chip);
69 }
70 
71 static void mchp_core_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm,
72 				 bool enable, u64 period)
73 {
74 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
75 	u8 channel_enable, reg_offset, shift;
76 
77 	/*
78 	 * There are two adjacent 8 bit control regs, the lower reg controls
79 	 * 0-7 and the upper reg 8-15. Check if the pwm is in the upper reg
80 	 * and if so, offset by the bus width.
81 	 */
82 	reg_offset = MCHPCOREPWM_EN(pwm->hwpwm >> 3);
83 	shift = pwm->hwpwm & 7;
84 
85 	channel_enable = readb_relaxed(mchp_core_pwm->base + reg_offset);
86 	channel_enable &= ~(1 << shift);
87 	channel_enable |= (enable << shift);
88 
89 	writel_relaxed(channel_enable, mchp_core_pwm->base + reg_offset);
90 	mchp_core_pwm->channel_enabled &= ~BIT(pwm->hwpwm);
91 	mchp_core_pwm->channel_enabled |= enable << pwm->hwpwm;
92 
93 	/*
94 	 * The updated values will not appear on the bus until they have been
95 	 * applied to the waveform at the beginning of the next period.
96 	 * This is a NO-OP if the channel does not have shadow registers.
97 	 */
98 	if (mchp_core_pwm->sync_update_mask & (1 << pwm->hwpwm))
99 		mchp_core_pwm->update_timestamp = ktime_add_ns(ktime_get(), period);
100 }
101 
102 static void mchp_core_pwm_wait_for_sync_update(struct mchp_core_pwm_chip *mchp_core_pwm,
103 					       unsigned int channel)
104 {
105 	/*
106 	 * If a shadow register is used for this PWM channel, and iff there is
107 	 * a pending update to the waveform, we must wait for it to be applied
108 	 * before attempting to read its state. Reading the registers yields
109 	 * the currently implemented settings & the new ones are only readable
110 	 * once the current period has ended.
111 	 */
112 
113 	if (mchp_core_pwm->sync_update_mask & (1 << channel)) {
114 		ktime_t current_time = ktime_get();
115 		s64 remaining_ns;
116 		u32 delay_us;
117 
118 		remaining_ns = ktime_to_ns(ktime_sub(mchp_core_pwm->update_timestamp,
119 						     current_time));
120 
121 		/*
122 		 * If the update has gone through, don't bother waiting for
123 		 * obvious reasons. Otherwise wait around for an appropriate
124 		 * amount of time for the update to go through.
125 		 */
126 		if (remaining_ns <= 0)
127 			return;
128 
129 		delay_us = DIV_ROUND_UP_ULL(remaining_ns, NSEC_PER_USEC);
130 		fsleep(delay_us);
131 	}
132 }
133 
134 static u64 mchp_core_pwm_calc_duty(const struct pwm_state *state, u64 clk_rate,
135 				   u8 prescale, u8 period_steps)
136 {
137 	u64 duty_steps, tmp;
138 
139 	/*
140 	 * Calculate the duty cycle in multiples of the prescaled period:
141 	 * duty_steps = duty_in_ns / step_in_ns
142 	 * step_in_ns = (prescale * NSEC_PER_SEC) / clk_rate
143 	 * The code below is rearranged slightly to only divide once.
144 	 */
145 	tmp = (((u64)prescale) + 1) * NSEC_PER_SEC;
146 	duty_steps = mul_u64_u64_div_u64(state->duty_cycle, clk_rate, tmp);
147 
148 	return duty_steps;
149 }
150 
151 static void mchp_core_pwm_apply_duty(struct pwm_chip *chip, struct pwm_device *pwm,
152 				     const struct pwm_state *state, u64 duty_steps,
153 				     u16 period_steps)
154 {
155 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
156 	u8 posedge, negedge;
157 	u8 first_edge = 0, second_edge = duty_steps;
158 
159 	/*
160 	 * Setting posedge == negedge doesn't yield a constant output,
161 	 * so that's an unsuitable setting to model duty_steps = 0.
162 	 * In that case set the unwanted edge to a value that never
163 	 * triggers.
164 	 */
165 	if (duty_steps == 0)
166 		first_edge = period_steps + 1;
167 
168 	if (state->polarity == PWM_POLARITY_INVERSED) {
169 		negedge = first_edge;
170 		posedge = second_edge;
171 	} else {
172 		posedge = first_edge;
173 		negedge = second_edge;
174 	}
175 
176 	/*
177 	 * Set the sync bit which ensures that periods that already started are
178 	 * completed unaltered. At each counter reset event the values are
179 	 * updated from the shadow registers.
180 	 */
181 	writel_relaxed(posedge, mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
182 	writel_relaxed(negedge, mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));
183 }
184 
185 static int mchp_core_pwm_calc_period(const struct pwm_state *state, unsigned long clk_rate,
186 				     u16 *prescale, u16 *period_steps)
187 {
188 	u64 tmp;
189 
190 	/*
191 	 * Calculate the period cycles and prescale values.
192 	 * The registers are each 8 bits wide & multiplied to compute the period
193 	 * using the formula:
194 	 *           (prescale + 1) * (period_steps + 1)
195 	 * period = -------------------------------------
196 	 *                      clk_rate
197 	 * so the maximum period that can be generated is 0x10000 times the
198 	 * period of the input clock.
199 	 * However, due to the design of the "hardware", it is not possible to
200 	 * attain a 100% duty cycle if the full range of period_steps is used.
201 	 * Therefore period_steps is restricted to 0xfe and the maximum multiple
202 	 * of the clock period attainable is (0xff + 1) * (0xfe + 1) = 0xff00
203 	 *
204 	 * The prescale and period_steps registers operate similarly to
205 	 * CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
206 	 * in the register plus one.
207 	 * It's therefore not possible to set a period lower than 1/clk_rate, so
208 	 * if tmp is 0, abort. Without aborting, we will set a period that is
209 	 * greater than that requested and, more importantly, will trigger the
210 	 * neg-/pos-edge issue described in the limitations.
211 	 */
212 	tmp = mul_u64_u64_div_u64(state->period, clk_rate, NSEC_PER_SEC);
213 	if (tmp >= MCHPCOREPWM_PERIOD_MAX) {
214 		*prescale = MCHPCOREPWM_PRESCALE_MAX;
215 		*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;
216 
217 		return 0;
218 	}
219 
220 	/*
221 	 * There are multiple strategies that could be used to choose the
222 	 * prescale & period_steps values.
223 	 * Here the idea is to pick values so that the selection of duty cycles
224 	 * is as finegrain as possible, while also keeping the period less than
225 	 * that requested.
226 	 *
227 	 * A simple way to satisfy the first condition is to always set
228 	 * period_steps to its maximum value. This neatly also satisfies the
229 	 * second condition too, since using the maximum value of period_steps
230 	 * to calculate prescale actually calculates its upper bound.
231 	 * Integer division will ensure a round down, so the period will thereby
232 	 * always be less than that requested.
233 	 *
234 	 * The downside of this approach is a significant degree of inaccuracy,
235 	 * especially as tmp approaches integer multiples of
236 	 * MCHPCOREPWM_PERIOD_STEPS_MAX.
237 	 *
238 	 * As we must produce a period less than that requested, and for the
239 	 * sake of creating a simple algorithm, disallow small values of tmp
240 	 * that would need special handling.
241 	 */
242 	if (tmp < MCHPCOREPWM_PERIOD_STEPS_MAX + 1)
243 		return -EINVAL;
244 
245 	/*
246 	 * This "optimal" value for prescale is be calculated using the maximum
247 	 * permitted value of period_steps, 0xfe.
248 	 *
249 	 *                period * clk_rate
250 	 * prescale = ------------------------- - 1
251 	 *            NSEC_PER_SEC * (0xfe + 1)
252 	 *
253 	 *
254 	 *  period * clk_rate
255 	 * ------------------- was precomputed as `tmp`
256 	 *    NSEC_PER_SEC
257 	 */
258 	*prescale = ((u16)tmp) / (MCHPCOREPWM_PERIOD_STEPS_MAX + 1) - 1;
259 
260 	/*
261 	 * period_steps can be computed from prescale:
262 	 *                      period * clk_rate
263 	 * period_steps = ----------------------------- - 1
264 	 *                NSEC_PER_SEC * (prescale + 1)
265 	 *
266 	 * However, in this approximation, we simply use the maximum value that
267 	 * was used to compute prescale.
268 	 */
269 	*period_steps = MCHPCOREPWM_PERIOD_STEPS_MAX;
270 
271 	return 0;
272 }
273 
274 static int mchp_core_pwm_apply_locked(struct pwm_chip *chip, struct pwm_device *pwm,
275 				      const struct pwm_state *state)
276 {
277 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
278 	bool period_locked;
279 	unsigned long clk_rate;
280 	u64 duty_steps;
281 	u16 prescale, period_steps;
282 	int ret;
283 
284 	if (!state->enabled) {
285 		mchp_core_pwm_enable(chip, pwm, false, pwm->state.period);
286 		return 0;
287 	}
288 
289 	/*
290 	 * If clk_rate is too big, the following multiplication might overflow.
291 	 * However this is implausible, as the fabric of current FPGAs cannot
292 	 * provide clocks at a rate high enough.
293 	 */
294 	clk_rate = clk_get_rate(mchp_core_pwm->clk);
295 	if (clk_rate >= NSEC_PER_SEC)
296 		return -EINVAL;
297 
298 	ret = mchp_core_pwm_calc_period(state, clk_rate, &prescale, &period_steps);
299 	if (ret)
300 		return ret;
301 
302 	/*
303 	 * If the only thing that has changed is the duty cycle or the polarity,
304 	 * we can shortcut the calculations and just compute/apply the new duty
305 	 * cycle pos & neg edges
306 	 * As all the channels share the same period, do not allow it to be
307 	 * changed if any other channels are enabled.
308 	 * If the period is locked, it may not be possible to use a period
309 	 * less than that requested. In that case, we just abort.
310 	 */
311 	period_locked = mchp_core_pwm->channel_enabled & ~(1 << pwm->hwpwm);
312 
313 	if (period_locked) {
314 		u16 hw_prescale;
315 		u16 hw_period_steps;
316 
317 		hw_prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
318 		hw_period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);
319 
320 		if ((period_steps + 1) * (prescale + 1) <
321 		    (hw_period_steps + 1) * (hw_prescale + 1))
322 			return -EINVAL;
323 
324 		/*
325 		 * It is possible that something could have set the period_steps
326 		 * register to 0xff, which would prevent us from setting a 100%
327 		 * or 0% relative duty cycle, as explained above in
328 		 * mchp_core_pwm_calc_period().
329 		 * The period is locked and we cannot change this, so we abort.
330 		 */
331 		if (hw_period_steps == MCHPCOREPWM_PERIOD_STEPS_MAX)
332 			return -EINVAL;
333 
334 		prescale = hw_prescale;
335 		period_steps = hw_period_steps;
336 	}
337 
338 	duty_steps = mchp_core_pwm_calc_duty(state, clk_rate, prescale, period_steps);
339 
340 	/*
341 	 * Because the period is not per channel, it is possible that the
342 	 * requested duty cycle is longer than the period, in which case cap it
343 	 * to the period, IOW a 100% duty cycle.
344 	 */
345 	if (duty_steps > period_steps)
346 		duty_steps = period_steps + 1;
347 
348 	if (!period_locked) {
349 		writel_relaxed(prescale, mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
350 		writel_relaxed(period_steps, mchp_core_pwm->base + MCHPCOREPWM_PERIOD);
351 	}
352 
353 	mchp_core_pwm_apply_duty(chip, pwm, state, duty_steps, period_steps);
354 
355 	mchp_core_pwm_enable(chip, pwm, true, pwm->state.period);
356 
357 	return 0;
358 }
359 
360 static int mchp_core_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
361 			       const struct pwm_state *state)
362 {
363 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
364 	int ret;
365 
366 	mutex_lock(&mchp_core_pwm->lock);
367 
368 	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);
369 
370 	ret = mchp_core_pwm_apply_locked(chip, pwm, state);
371 
372 	mutex_unlock(&mchp_core_pwm->lock);
373 
374 	return ret;
375 }
376 
377 static int mchp_core_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
378 				   struct pwm_state *state)
379 {
380 	struct mchp_core_pwm_chip *mchp_core_pwm = to_mchp_core_pwm(chip);
381 	u64 rate;
382 	u16 prescale, period_steps;
383 	u8 duty_steps, posedge, negedge;
384 
385 	mutex_lock(&mchp_core_pwm->lock);
386 
387 	mchp_core_pwm_wait_for_sync_update(mchp_core_pwm, pwm->hwpwm);
388 
389 	if (mchp_core_pwm->channel_enabled & (1 << pwm->hwpwm))
390 		state->enabled = true;
391 	else
392 		state->enabled = false;
393 
394 	rate = clk_get_rate(mchp_core_pwm->clk);
395 
396 	/*
397 	 * Calculating the period:
398 	 * The registers are each 8 bits wide & multiplied to compute the period
399 	 * using the formula:
400 	 *           (prescale + 1) * (period_steps + 1)
401 	 * period = -------------------------------------
402 	 *                      clk_rate
403 	 *
404 	 * Note:
405 	 * The prescale and period_steps registers operate similarly to
406 	 * CLK_DIVIDER_ONE_BASED, where the value used by the hardware is that
407 	 * in the register plus one.
408 	 */
409 	prescale = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PRESCALE);
410 	period_steps = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_PERIOD);
411 
412 	state->period = (period_steps + 1) * (prescale + 1);
413 	state->period *= NSEC_PER_SEC;
414 	state->period = DIV64_U64_ROUND_UP(state->period, rate);
415 
416 	posedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_POSEDGE(pwm->hwpwm));
417 	negedge = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_NEGEDGE(pwm->hwpwm));
418 
419 	mutex_unlock(&mchp_core_pwm->lock);
420 
421 	if (negedge == posedge) {
422 		state->duty_cycle = state->period;
423 		state->period *= 2;
424 	} else {
425 		duty_steps = abs((s16)posedge - (s16)negedge);
426 		state->duty_cycle = duty_steps * (prescale + 1) * NSEC_PER_SEC;
427 		state->duty_cycle = DIV64_U64_ROUND_UP(state->duty_cycle, rate);
428 	}
429 
430 	state->polarity = negedge < posedge ? PWM_POLARITY_INVERSED : PWM_POLARITY_NORMAL;
431 
432 	return 0;
433 }
434 
435 static const struct pwm_ops mchp_core_pwm_ops = {
436 	.apply = mchp_core_pwm_apply,
437 	.get_state = mchp_core_pwm_get_state,
438 	.owner = THIS_MODULE,
439 };
440 
441 static const struct of_device_id mchp_core_of_match[] = {
442 	{
443 		.compatible = "microchip,corepwm-rtl-v4",
444 	},
445 	{ /* sentinel */ }
446 };
447 MODULE_DEVICE_TABLE(of, mchp_core_of_match);
448 
449 static int mchp_core_pwm_probe(struct platform_device *pdev)
450 {
451 	struct mchp_core_pwm_chip *mchp_core_pwm;
452 	struct resource *regs;
453 	int ret;
454 
455 	mchp_core_pwm = devm_kzalloc(&pdev->dev, sizeof(*mchp_core_pwm), GFP_KERNEL);
456 	if (!mchp_core_pwm)
457 		return -ENOMEM;
458 
459 	mchp_core_pwm->base = devm_platform_get_and_ioremap_resource(pdev, 0, &regs);
460 	if (IS_ERR(mchp_core_pwm->base))
461 		return PTR_ERR(mchp_core_pwm->base);
462 
463 	mchp_core_pwm->clk = devm_clk_get_enabled(&pdev->dev, NULL);
464 	if (IS_ERR(mchp_core_pwm->clk))
465 		return dev_err_probe(&pdev->dev, PTR_ERR(mchp_core_pwm->clk),
466 				     "failed to get PWM clock\n");
467 
468 	if (of_property_read_u32(pdev->dev.of_node, "microchip,sync-update-mask",
469 				 &mchp_core_pwm->sync_update_mask))
470 		mchp_core_pwm->sync_update_mask = 0;
471 
472 	mutex_init(&mchp_core_pwm->lock);
473 
474 	mchp_core_pwm->chip.dev = &pdev->dev;
475 	mchp_core_pwm->chip.ops = &mchp_core_pwm_ops;
476 	mchp_core_pwm->chip.npwm = 16;
477 
478 	mchp_core_pwm->channel_enabled = readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(0));
479 	mchp_core_pwm->channel_enabled |=
480 		readb_relaxed(mchp_core_pwm->base + MCHPCOREPWM_EN(1)) << 8;
481 
482 	/*
483 	 * Enable synchronous update mode for all channels for which shadow
484 	 * registers have been synthesised.
485 	 */
486 	writel_relaxed(1U, mchp_core_pwm->base + MCHPCOREPWM_SYNC_UPD);
487 	mchp_core_pwm->update_timestamp = ktime_get();
488 
489 	ret = devm_pwmchip_add(&pdev->dev, &mchp_core_pwm->chip);
490 	if (ret)
491 		return dev_err_probe(&pdev->dev, ret, "Failed to add pwmchip\n");
492 
493 	return 0;
494 }
495 
496 static struct platform_driver mchp_core_pwm_driver = {
497 	.driver = {
498 		.name = "mchp-core-pwm",
499 		.of_match_table = mchp_core_of_match,
500 	},
501 	.probe = mchp_core_pwm_probe,
502 };
503 module_platform_driver(mchp_core_pwm_driver);
504 
505 MODULE_LICENSE("GPL");
506 MODULE_AUTHOR("Conor Dooley <conor.dooley@microchip.com>");
507 MODULE_DESCRIPTION("corePWM driver for Microchip FPGAs");
508