1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (c) 2019 Western Digital Corporation or its affiliates.
5 * Copyright (C) 2018 SiFive, Inc.
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License version 2 as
11 * published by the Free Software Foundation.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * This library supports configuration parsing and reprogramming of
19 * the CLN28HPC variant of the Analog Bits Wide Range PLL. The
20 * intention is for this library to be reusable for any device that
21 * integrates this PLL; thus the register structure and programming
22 * details are expected to be provided by a separate IP block driver.
24 * The bulk of this code is primarily useful for clock configurations
25 * that must operate at arbitrary rates, as opposed to clock configurations
26 * that are restricted by software or manufacturer guidance to a small,
27 * pre-determined set of performance points.
30 * - Analog Bits "Wide Range PLL Datasheet", version 2015.10.01
31 * - SiFive FU540-C000 Manual v1p0, Chapter 7 "Clocking and Reset"
34 #include <linux/bug.h>
35 #include <linux/err.h>
36 #include <linux/log2.h>
37 #include <linux/math64.h>
38 #include <linux/clk/analogbits-wrpll-cln28hpc.h>
40 /* MIN_INPUT_FREQ: minimum input clock frequency, in Hz (Fref_min) */
41 #define MIN_INPUT_FREQ 7000000
43 /* MAX_INPUT_FREQ: maximum input clock frequency, in Hz (Fref_max) */
44 #define MAX_INPUT_FREQ 600000000
46 /* MIN_POST_DIVIDE_REF_FREQ: minimum post-divider reference frequency, in Hz */
47 #define MIN_POST_DIVR_FREQ 7000000
49 /* MAX_POST_DIVIDE_REF_FREQ: maximum post-divider reference frequency, in Hz */
50 #define MAX_POST_DIVR_FREQ 200000000
52 /* MIN_VCO_FREQ: minimum VCO frequency, in Hz (Fvco_min) */
53 #define MIN_VCO_FREQ 2400000000UL
55 /* MAX_VCO_FREQ: maximum VCO frequency, in Hz (Fvco_max) */
56 #define MAX_VCO_FREQ 4800000000ULL
58 /* MAX_DIVQ_DIVISOR: maximum output divisor. Selected by DIVQ = 6 */
59 #define MAX_DIVQ_DIVISOR 64
61 /* MAX_DIVR_DIVISOR: maximum reference divisor. Selected by DIVR = 63 */
62 #define MAX_DIVR_DIVISOR 64
64 /* MAX_LOCK_US: maximum PLL lock time, in microseconds (tLOCK_max) */
65 #define MAX_LOCK_US 70
68 * ROUND_SHIFT: number of bits to shift to avoid precision loss in the rounding
71 #define ROUND_SHIFT 20
78 * __wrpll_calc_filter_range() - determine PLL loop filter bandwidth
79 * @post_divr_freq: input clock rate after the R divider
81 * Select the value to be presented to the PLL RANGE input signals, based
82 * on the input clock frequency after the post-R-divider @post_divr_freq.
83 * This code follows the recommendations in the PLL datasheet for filter
86 * Return: The RANGE value to be presented to the PLL configuration inputs,
89 static int __wrpll_calc_filter_range(unsigned long post_divr_freq)
93 if (post_divr_freq < MIN_POST_DIVR_FREQ ||
94 post_divr_freq > MAX_POST_DIVR_FREQ) {
95 WARN(1, "%s: post-divider reference freq out of range: %lu",
96 __func__, post_divr_freq);
100 if (post_divr_freq < 11000000)
102 else if (post_divr_freq < 18000000)
104 else if (post_divr_freq < 30000000)
106 else if (post_divr_freq < 50000000)
108 else if (post_divr_freq < 80000000)
110 else if (post_divr_freq < 130000000)
119 * __wrpll_calc_fbdiv() - return feedback fixed divide value
120 * @c: ptr to a struct analogbits_wrpll_cfg record to read from
122 * The internal feedback path includes a fixed by-two divider; the
123 * external feedback path does not. Return the appropriate divider
124 * value (2 or 1) depending on whether internal or external feedback
125 * is enabled. This code doesn't test for invalid configurations
126 * (e.g. both or neither of WRPLL_FLAGS_*_FEEDBACK are set); it relies
127 * on the caller to do so.
129 * Context: Any context. Caller must protect the memory pointed to by
130 * @c from simultaneous modification.
132 * Return: 2 if internal feedback is enabled or 1 if external feedback
135 static u8 __wrpll_calc_fbdiv(struct analogbits_wrpll_cfg *c)
137 return (c->flags & WRPLL_FLAGS_INT_FEEDBACK_MASK) ? 2 : 1;
141 * __wrpll_calc_divq() - determine DIVQ based on target PLL output clock rate
142 * @target_rate: target PLL output clock rate
143 * @vco_rate: pointer to a u64 to store the computed VCO rate into
145 * Determine a reasonable value for the PLL Q post-divider, based on the
146 * target output rate @target_rate for the PLL. Along with returning the
147 * computed Q divider value as the return value, this function stores the
148 * desired target VCO rate into the variable pointed to by @vco_rate.
150 * Context: Any context. Caller must protect the memory pointed to by
151 * @vco_rate from simultaneous access or modification.
153 * Return: a positive integer DIVQ value to be programmed into the hardware
154 * upon success, or 0 upon error (since 0 is an invalid DIVQ value)
156 static u8 __wrpll_calc_divq(u32 target_rate, u64 *vco_rate)
166 s = div_u64(MAX_VCO_FREQ, target_rate);
169 *vco_rate = MAX_VCO_FREQ;
170 } else if (s > MAX_DIVQ_DIVISOR) {
171 divq = ilog2(MAX_DIVQ_DIVISOR);
172 *vco_rate = MIN_VCO_FREQ;
175 *vco_rate = target_rate << divq;
183 * __wrpll_update_parent_rate() - update PLL data when parent rate changes
184 * @c: ptr to a struct analogbits_wrpll_cfg record to write PLL data to
185 * @parent_rate: PLL input refclk rate (pre-R-divider)
187 * Pre-compute some data used by the PLL configuration algorithm when
188 * the PLL's reference clock rate changes. The intention is to avoid
189 * computation when the parent rate remains constant - expected to be
192 * Returns: 0 upon success or -1 if the reference clock rate is out of range.
194 static int __wrpll_update_parent_rate(struct analogbits_wrpll_cfg *c,
195 unsigned long parent_rate)
199 if (parent_rate > MAX_INPUT_FREQ || parent_rate < MIN_POST_DIVR_FREQ)
202 c->_parent_rate = parent_rate;
203 max_r_for_parent = div_u64(parent_rate, MIN_POST_DIVR_FREQ);
204 c->_max_r = min_t(u8, MAX_DIVR_DIVISOR, max_r_for_parent);
207 c->_init_r = div_u64(parent_rate + MAX_POST_DIVR_FREQ - 1,
218 * analogbits_wrpll_configure() - compute PLL configuration for a target rate
219 * @c: ptr to a struct analogbits_wrpll_cfg record to write into
220 * @target_rate: target PLL output clock rate (post-Q-divider)
221 * @parent_rate: PLL input refclk rate (pre-R-divider)
223 * Given a pointer to a PLL context @c, a desired PLL target output
224 * rate @target_rate, and a reference clock input rate @parent_rate,
225 * compute the appropriate PLL signal configuration values. PLL
226 * reprogramming is not glitchless, so the caller should switch any
227 * downstream logic to a different clock source or clock-gate it
228 * before presenting these values to the PLL configuration signals.
230 * The caller must pass this function a pre-initialized struct
231 * analogbits_wrpll_cfg record: either initialized to zero (with the
232 * exception of the .name and .flags fields) or read from the PLL.
234 * Context: Any context. Caller must protect the memory pointed to by @c
235 * from simultaneous access or modification.
237 * Return: 0 upon success; anything else upon failure.
239 int analogbits_wrpll_configure_for_rate(struct analogbits_wrpll_cfg *c,
241 unsigned long parent_rate)
244 u64 target_vco_rate, delta, best_delta, f_pre_div, vco, vco_pre;
245 u32 best_f, f, post_divr_freq, fbcfg;
246 u8 fbdiv, divq, best_r, r;
252 WARN(1, "%s called with uninitialized PLL config", __func__);
256 fbcfg = WRPLL_FLAGS_INT_FEEDBACK_MASK | WRPLL_FLAGS_EXT_FEEDBACK_MASK;
257 if ((c->flags & fbcfg) == fbcfg) {
258 WARN(1, "%s called with invalid PLL config", __func__);
262 if (c->flags == WRPLL_FLAGS_EXT_FEEDBACK_MASK) {
263 WARN(1, "%s: external feedback mode not currently supported",
268 /* Initialize rounding data if it hasn't been initialized already */
269 if (parent_rate != c->_parent_rate) {
270 if (__wrpll_update_parent_rate(c, parent_rate)) {
271 pr_err("%s: PLL input rate is out of range\n",
277 c->flags &= ~WRPLL_FLAGS_RESET_MASK;
279 /* Put the PLL into bypass if the user requests the parent clock rate */
280 if (target_rate == parent_rate) {
281 c->flags |= WRPLL_FLAGS_BYPASS_MASK;
284 c->flags &= ~WRPLL_FLAGS_BYPASS_MASK;
286 /* Calculate the Q shift and target VCO rate */
287 divq = __wrpll_calc_divq(target_rate, &target_vco_rate);
292 /* Precalculate the pre-Q divider target ratio */
293 ratio = div64_u64((target_vco_rate << ROUND_SHIFT), parent_rate);
295 fbdiv = __wrpll_calc_fbdiv(c);
298 best_delta = MAX_VCO_FREQ;
301 * Consider all values for R which land within
302 * [MIN_POST_DIVR_FREQ, MAX_POST_DIVR_FREQ]; prefer smaller R
304 for (r = c->_init_r; r <= c->_max_r; ++r) {
305 /* What is the best F we can pick in this case? */
306 f_pre_div = ratio * r;
307 f = (f_pre_div + (1 << ROUND_SHIFT)) >> ROUND_SHIFT;
310 post_divr_freq = div_u64(parent_rate, r);
311 vco_pre = fbdiv * post_divr_freq;
314 /* Ensure rounding didn't take us out of range */
315 if (vco > target_vco_rate) {
318 } else if (vco < MIN_VCO_FREQ) {
323 delta = abs(target_rate - vco);
324 if (delta < best_delta) {
331 c->divr = best_r - 1;
332 c->divf = best_f - 1;
334 post_divr_freq = div_u64(parent_rate, best_r);
336 /* Pick the best PLL jitter filter */
337 c->range = __wrpll_calc_filter_range(post_divr_freq);
343 * analogbits_wrpll_calc_output_rate() - calculate the PLL's target output rate
344 * @c: ptr to a struct analogbits_wrpll_cfg record to read from
345 * @parent_rate: PLL refclk rate
347 * Given a pointer to the PLL's current input configuration @c and the
348 * PLL's input reference clock rate @parent_rate (before the R
349 * pre-divider), calculate the PLL's output clock rate (after the Q
352 * Context: Any context. Caller must protect the memory pointed to by @c
353 * from simultaneous modification.
355 * Return: the PLL's output clock rate, in Hz.
357 unsigned long analogbits_wrpll_calc_output_rate(struct analogbits_wrpll_cfg *c,
358 unsigned long parent_rate)
363 WARN(c->flags & WRPLL_FLAGS_EXT_FEEDBACK_MASK,
364 "external feedback mode not yet supported");
366 fbdiv = __wrpll_calc_fbdiv(c);
367 n = parent_rate * fbdiv * (c->divf + 1);
368 n = div_u64(n, (c->divr + 1));
375 * analogbits_wrpll_calc_max_lock_us() - return the time for the PLL to lock
376 * @c: ptr to a struct analogbits_wrpll_cfg record to read from
378 * Return the minimum amount of time (in microseconds) that the caller
379 * must wait after reprogramming the PLL to ensure that it is locked
380 * to the input frequency and stable. This is likely to depend on the DIVR
381 * value; this is under discussion with the manufacturer.
383 * Return: the minimum amount of time the caller must wait for the PLL
384 * to lock (in microseconds)
386 unsigned int analogbits_wrpll_calc_max_lock_us(struct analogbits_wrpll_cfg *c)