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_device.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, ®s); 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