1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 2018-2019 SiFive, Inc.
4 * Wesley Terpstra
5 * Paul Walmsley
6 *
7 * This library supports configuration parsing and reprogramming of
8 * the CLN28HPC variant of the Analog Bits Wide Range PLL. The
9 * intention is for this library to be reusable for any device that
10 * integrates this PLL; thus the register structure and programming
11 * details are expected to be provided by a separate IP block driver.
12 *
13 * The bulk of this code is primarily useful for clock configurations
14 * that must operate at arbitrary rates, as opposed to clock configurations
15 * that are restricted by software or manufacturer guidance to a small,
16 * pre-determined set of performance points.
17 *
18 * References:
19 * - Analog Bits "Wide Range PLL Datasheet", version 2015.10.01
20 * - SiFive FU540-C000 Manual v1p0, Chapter 7 "Clocking and Reset"
21 * https://static.dev.sifive.com/FU540-C000-v1.0.pdf
22 */
23
24 #include <linux/bug.h>
25 #include <linux/err.h>
26 #include <linux/limits.h>
27 #include <linux/log2.h>
28 #include <linux/math64.h>
29 #include <linux/math.h>
30 #include <linux/minmax.h>
31 #include <linux/module.h>
32
33 #include <linux/clk/analogbits-wrpll-cln28hpc.h>
34
35 /* MIN_INPUT_FREQ: minimum input clock frequency, in Hz (Fref_min) */
36 #define MIN_INPUT_FREQ 7000000
37
38 /* MAX_INPUT_FREQ: maximum input clock frequency, in Hz (Fref_max) */
39 #define MAX_INPUT_FREQ 600000000
40
41 /* MIN_POST_DIVIDE_REF_FREQ: minimum post-divider reference frequency, in Hz */
42 #define MIN_POST_DIVR_FREQ 7000000
43
44 /* MAX_POST_DIVIDE_REF_FREQ: maximum post-divider reference frequency, in Hz */
45 #define MAX_POST_DIVR_FREQ 200000000
46
47 /* MIN_VCO_FREQ: minimum VCO frequency, in Hz (Fvco_min) */
48 #define MIN_VCO_FREQ 2400000000UL
49
50 /* MAX_VCO_FREQ: maximum VCO frequency, in Hz (Fvco_max) */
51 #define MAX_VCO_FREQ 4800000000ULL
52
53 /* MAX_DIVQ_DIVISOR: maximum output divisor. Selected by DIVQ = 6 */
54 #define MAX_DIVQ_DIVISOR 64
55
56 /* MAX_DIVR_DIVISOR: maximum reference divisor. Selected by DIVR = 63 */
57 #define MAX_DIVR_DIVISOR 64
58
59 /* MAX_LOCK_US: maximum PLL lock time, in microseconds (tLOCK_max) */
60 #define MAX_LOCK_US 70
61
62 /*
63 * ROUND_SHIFT: number of bits to shift to avoid precision loss in the rounding
64 * algorithm
65 */
66 #define ROUND_SHIFT 20
67
68 /*
69 * Private functions
70 */
71
72 /**
73 * __wrpll_calc_filter_range() - determine PLL loop filter bandwidth
74 * @post_divr_freq: input clock rate after the R divider
75 *
76 * Select the value to be presented to the PLL RANGE input signals, based
77 * on the input clock frequency after the post-R-divider @post_divr_freq.
78 * This code follows the recommendations in the PLL datasheet for filter
79 * range selection.
80 *
81 * Return: The RANGE value to be presented to the PLL configuration inputs,
82 * or a negative return code upon error.
83 */
__wrpll_calc_filter_range(unsigned long post_divr_freq)84 static int __wrpll_calc_filter_range(unsigned long post_divr_freq)
85 {
86 if (post_divr_freq < MIN_POST_DIVR_FREQ ||
87 post_divr_freq > MAX_POST_DIVR_FREQ) {
88 WARN(1, "%s: post-divider reference freq out of range: %lu",
89 __func__, post_divr_freq);
90 return -ERANGE;
91 }
92
93 switch (post_divr_freq) {
94 case 0 ... 10999999:
95 return 1;
96 case 11000000 ... 17999999:
97 return 2;
98 case 18000000 ... 29999999:
99 return 3;
100 case 30000000 ... 49999999:
101 return 4;
102 case 50000000 ... 79999999:
103 return 5;
104 case 80000000 ... 129999999:
105 return 6;
106 }
107
108 return 7;
109 }
110
111 /**
112 * __wrpll_calc_fbdiv() - return feedback fixed divide value
113 * @c: ptr to a struct wrpll_cfg record to read from
114 *
115 * The internal feedback path includes a fixed by-two divider; the
116 * external feedback path does not. Return the appropriate divider
117 * value (2 or 1) depending on whether internal or external feedback
118 * is enabled. This code doesn't test for invalid configurations
119 * (e.g. both or neither of WRPLL_FLAGS_*_FEEDBACK are set); it relies
120 * on the caller to do so.
121 *
122 * Context: Any context. Caller must protect the memory pointed to by
123 * @c from simultaneous modification.
124 *
125 * Return: 2 if internal feedback is enabled or 1 if external feedback
126 * is enabled.
127 */
__wrpll_calc_fbdiv(const struct wrpll_cfg * c)128 static u8 __wrpll_calc_fbdiv(const struct wrpll_cfg *c)
129 {
130 return (c->flags & WRPLL_FLAGS_INT_FEEDBACK_MASK) ? 2 : 1;
131 }
132
133 /**
134 * __wrpll_calc_divq() - determine DIVQ based on target PLL output clock rate
135 * @target_rate: target PLL output clock rate
136 * @vco_rate: pointer to a u64 to store the computed VCO rate into
137 *
138 * Determine a reasonable value for the PLL Q post-divider, based on the
139 * target output rate @target_rate for the PLL. Along with returning the
140 * computed Q divider value as the return value, this function stores the
141 * desired target VCO rate into the variable pointed to by @vco_rate.
142 *
143 * Context: Any context. Caller must protect the memory pointed to by
144 * @vco_rate from simultaneous access or modification.
145 *
146 * Return: a positive integer DIVQ value to be programmed into the hardware
147 * upon success, or 0 upon error (since 0 is an invalid DIVQ value)
148 */
__wrpll_calc_divq(u32 target_rate,u64 * vco_rate)149 static u8 __wrpll_calc_divq(u32 target_rate, u64 *vco_rate)
150 {
151 u64 s;
152 u8 divq = 0;
153
154 if (!vco_rate) {
155 WARN_ON(1);
156 goto wcd_out;
157 }
158
159 s = div_u64(MAX_VCO_FREQ, target_rate);
160 if (s <= 1) {
161 divq = 1;
162 *vco_rate = MAX_VCO_FREQ;
163 } else if (s > MAX_DIVQ_DIVISOR) {
164 divq = ilog2(MAX_DIVQ_DIVISOR);
165 *vco_rate = MIN_VCO_FREQ;
166 } else {
167 divq = ilog2(s);
168 *vco_rate = (u64)target_rate << divq;
169 }
170
171 wcd_out:
172 return divq;
173 }
174
175 /**
176 * __wrpll_update_parent_rate() - update PLL data when parent rate changes
177 * @c: ptr to a struct wrpll_cfg record to write PLL data to
178 * @parent_rate: PLL input refclk rate (pre-R-divider)
179 *
180 * Pre-compute some data used by the PLL configuration algorithm when
181 * the PLL's reference clock rate changes. The intention is to avoid
182 * computation when the parent rate remains constant - expected to be
183 * the common case.
184 *
185 * Returns: 0 upon success or -ERANGE if the reference clock rate is
186 * out of range.
187 */
__wrpll_update_parent_rate(struct wrpll_cfg * c,unsigned long parent_rate)188 static int __wrpll_update_parent_rate(struct wrpll_cfg *c,
189 unsigned long parent_rate)
190 {
191 u8 max_r_for_parent;
192
193 if (parent_rate > MAX_INPUT_FREQ || parent_rate < MIN_POST_DIVR_FREQ)
194 return -ERANGE;
195
196 c->parent_rate = parent_rate;
197 max_r_for_parent = div_u64(parent_rate, MIN_POST_DIVR_FREQ);
198 c->max_r = min_t(u8, MAX_DIVR_DIVISOR, max_r_for_parent);
199
200 c->init_r = DIV_ROUND_UP_ULL(parent_rate, MAX_POST_DIVR_FREQ);
201
202 return 0;
203 }
204
205 /**
206 * wrpll_configure_for_rate() - compute PLL configuration for a target rate
207 * @c: ptr to a struct wrpll_cfg record to write into
208 * @target_rate: target PLL output clock rate (post-Q-divider)
209 * @parent_rate: PLL input refclk rate (pre-R-divider)
210 *
211 * Compute the appropriate PLL signal configuration values and store
212 * in PLL context @c. PLL reprogramming is not glitchless, so the
213 * caller should switch any downstream logic to a different clock
214 * source or clock-gate it before presenting these values to the PLL
215 * configuration signals.
216 *
217 * The caller must pass this function a pre-initialized struct
218 * wrpll_cfg record: either initialized to zero (with the
219 * exception of the .name and .flags fields) or read from the PLL.
220 *
221 * Context: Any context. Caller must protect the memory pointed to by @c
222 * from simultaneous access or modification.
223 *
224 * Return: 0 upon success; anything else upon failure.
225 */
wrpll_configure_for_rate(struct wrpll_cfg * c,u32 target_rate,unsigned long parent_rate)226 int wrpll_configure_for_rate(struct wrpll_cfg *c, u32 target_rate,
227 unsigned long parent_rate)
228 {
229 unsigned long ratio;
230 u64 target_vco_rate, delta, best_delta, f_pre_div, vco, vco_pre;
231 u32 best_f, f, post_divr_freq;
232 u8 fbdiv, divq, best_r, r;
233 int range;
234
235 if (c->flags == 0) {
236 WARN(1, "%s called with uninitialized PLL config", __func__);
237 return -EINVAL;
238 }
239
240 /* Initialize rounding data if it hasn't been initialized already */
241 if (parent_rate != c->parent_rate) {
242 if (__wrpll_update_parent_rate(c, parent_rate)) {
243 pr_err("%s: PLL input rate is out of range\n",
244 __func__);
245 return -ERANGE;
246 }
247 }
248
249 c->flags &= ~WRPLL_FLAGS_RESET_MASK;
250
251 /* Put the PLL into bypass if the user requests the parent clock rate */
252 if (target_rate == parent_rate) {
253 c->flags |= WRPLL_FLAGS_BYPASS_MASK;
254 return 0;
255 }
256
257 c->flags &= ~WRPLL_FLAGS_BYPASS_MASK;
258
259 /* Calculate the Q shift and target VCO rate */
260 divq = __wrpll_calc_divq(target_rate, &target_vco_rate);
261 if (!divq)
262 return -1;
263 c->divq = divq;
264
265 /* Precalculate the pre-Q divider target ratio */
266 ratio = div64_u64((target_vco_rate << ROUND_SHIFT), parent_rate);
267
268 fbdiv = __wrpll_calc_fbdiv(c);
269 best_r = 0;
270 best_f = 0;
271 best_delta = MAX_VCO_FREQ;
272
273 /*
274 * Consider all values for R which land within
275 * [MIN_POST_DIVR_FREQ, MAX_POST_DIVR_FREQ]; prefer smaller R
276 */
277 for (r = c->init_r; r <= c->max_r; ++r) {
278 f_pre_div = ratio * r;
279 f = (f_pre_div + (1 << ROUND_SHIFT)) >> ROUND_SHIFT;
280 f >>= (fbdiv - 1);
281
282 post_divr_freq = div_u64(parent_rate, r);
283 vco_pre = fbdiv * post_divr_freq;
284 vco = vco_pre * f;
285
286 /* Ensure rounding didn't take us out of range */
287 if (vco > target_vco_rate) {
288 --f;
289 vco = vco_pre * f;
290 } else if (vco < MIN_VCO_FREQ) {
291 ++f;
292 vco = vco_pre * f;
293 }
294
295 delta = abs(target_rate - vco);
296 if (delta < best_delta) {
297 best_delta = delta;
298 best_r = r;
299 best_f = f;
300 }
301 }
302
303 c->divr = best_r - 1;
304 c->divf = best_f - 1;
305
306 post_divr_freq = div_u64(parent_rate, best_r);
307
308 /* Pick the best PLL jitter filter */
309 range = __wrpll_calc_filter_range(post_divr_freq);
310 if (range < 0)
311 return range;
312 c->range = range;
313
314 return 0;
315 }
316 EXPORT_SYMBOL_GPL(wrpll_configure_for_rate);
317
318 /**
319 * wrpll_calc_output_rate() - calculate the PLL's target output rate
320 * @c: ptr to a struct wrpll_cfg record to read from
321 * @parent_rate: PLL refclk rate
322 *
323 * Given a pointer to the PLL's current input configuration @c and the
324 * PLL's input reference clock rate @parent_rate (before the R
325 * pre-divider), calculate the PLL's output clock rate (after the Q
326 * post-divider).
327 *
328 * Context: Any context. Caller must protect the memory pointed to by @c
329 * from simultaneous modification.
330 *
331 * Return: the PLL's output clock rate, in Hz. The return value from
332 * this function is intended to be convenient to pass directly
333 * to the Linux clock framework; thus there is no explicit
334 * error return value.
335 */
wrpll_calc_output_rate(const struct wrpll_cfg * c,unsigned long parent_rate)336 unsigned long wrpll_calc_output_rate(const struct wrpll_cfg *c,
337 unsigned long parent_rate)
338 {
339 u8 fbdiv;
340 u64 n;
341
342 if (c->flags & WRPLL_FLAGS_EXT_FEEDBACK_MASK) {
343 WARN(1, "external feedback mode not yet supported");
344 return ULONG_MAX;
345 }
346
347 fbdiv = __wrpll_calc_fbdiv(c);
348 n = parent_rate * fbdiv * (c->divf + 1);
349 n = div_u64(n, c->divr + 1);
350 n >>= c->divq;
351
352 return n;
353 }
354 EXPORT_SYMBOL_GPL(wrpll_calc_output_rate);
355
356 /**
357 * wrpll_calc_max_lock_us() - return the time for the PLL to lock
358 * @c: ptr to a struct wrpll_cfg record to read from
359 *
360 * Return the minimum amount of time (in microseconds) that the caller
361 * must wait after reprogramming the PLL to ensure that it is locked
362 * to the input frequency and stable. This is likely to depend on the DIVR
363 * value; this is under discussion with the manufacturer.
364 *
365 * Return: the minimum amount of time the caller must wait for the PLL
366 * to lock (in microseconds)
367 */
wrpll_calc_max_lock_us(const struct wrpll_cfg * c)368 unsigned int wrpll_calc_max_lock_us(const struct wrpll_cfg *c)
369 {
370 return MAX_LOCK_US;
371 }
372 EXPORT_SYMBOL_GPL(wrpll_calc_max_lock_us);
373
374 MODULE_AUTHOR("Paul Walmsley <paul.walmsley@sifive.com>");
375 MODULE_DESCRIPTION("Analog Bits Wide-Range PLL library");
376 MODULE_LICENSE("GPL");
377