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![Anup Patel](/assets/img/avatar_default.png)
Now that SiFive clock driver is merged in upstream Linux, we sync-up WRPLL library used by SiFive clock driver with upstream Linux sources. Signed-off-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
365 lines
11 KiB
C
365 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2018-2019 SiFive, Inc.
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* Wesley Terpstra
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* Paul Walmsley
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*
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* This library supports configuration parsing and reprogramming of
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* the CLN28HPC variant of the Analog Bits Wide Range PLL. The
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* intention is for this library to be reusable for any device that
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* integrates this PLL; thus the register structure and programming
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* details are expected to be provided by a separate IP block driver.
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*
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* The bulk of this code is primarily useful for clock configurations
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* that must operate at arbitrary rates, as opposed to clock configurations
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* that are restricted by software or manufacturer guidance to a small,
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* pre-determined set of performance points.
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*
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* References:
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* - Analog Bits "Wide Range PLL Datasheet", version 2015.10.01
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* - SiFive FU540-C000 Manual v1p0, Chapter 7 "Clocking and Reset"
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* https://static.dev.sifive.com/FU540-C000-v1.0.pdf
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*/
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#include <linux/bug.h>
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#include <linux/err.h>
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#include <linux/log2.h>
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#include <linux/math64.h>
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#include <linux/clk/analogbits-wrpll-cln28hpc.h>
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/* MIN_INPUT_FREQ: minimum input clock frequency, in Hz (Fref_min) */
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#define MIN_INPUT_FREQ 7000000
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/* MAX_INPUT_FREQ: maximum input clock frequency, in Hz (Fref_max) */
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#define MAX_INPUT_FREQ 600000000
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/* MIN_POST_DIVIDE_REF_FREQ: minimum post-divider reference frequency, in Hz */
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#define MIN_POST_DIVR_FREQ 7000000
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/* MAX_POST_DIVIDE_REF_FREQ: maximum post-divider reference frequency, in Hz */
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#define MAX_POST_DIVR_FREQ 200000000
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/* MIN_VCO_FREQ: minimum VCO frequency, in Hz (Fvco_min) */
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#define MIN_VCO_FREQ 2400000000UL
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/* MAX_VCO_FREQ: maximum VCO frequency, in Hz (Fvco_max) */
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#define MAX_VCO_FREQ 4800000000ULL
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/* MAX_DIVQ_DIVISOR: maximum output divisor. Selected by DIVQ = 6 */
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#define MAX_DIVQ_DIVISOR 64
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/* MAX_DIVR_DIVISOR: maximum reference divisor. Selected by DIVR = 63 */
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#define MAX_DIVR_DIVISOR 64
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/* MAX_LOCK_US: maximum PLL lock time, in microseconds (tLOCK_max) */
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#define MAX_LOCK_US 70
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/*
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* ROUND_SHIFT: number of bits to shift to avoid precision loss in the rounding
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* algorithm
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*/
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#define ROUND_SHIFT 20
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/*
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* Private functions
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*/
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/**
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* __wrpll_calc_filter_range() - determine PLL loop filter bandwidth
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* @post_divr_freq: input clock rate after the R divider
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*
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* Select the value to be presented to the PLL RANGE input signals, based
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* on the input clock frequency after the post-R-divider @post_divr_freq.
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* This code follows the recommendations in the PLL datasheet for filter
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* range selection.
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*
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* Return: The RANGE value to be presented to the PLL configuration inputs,
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* or a negative return code upon error.
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*/
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static int __wrpll_calc_filter_range(unsigned long post_divr_freq)
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{
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if (post_divr_freq < MIN_POST_DIVR_FREQ ||
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post_divr_freq > MAX_POST_DIVR_FREQ) {
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WARN(1, "%s: post-divider reference freq out of range: %lu",
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__func__, post_divr_freq);
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return -ERANGE;
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}
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switch (post_divr_freq) {
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case 0 ... 10999999:
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return 1;
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case 11000000 ... 17999999:
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return 2;
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case 18000000 ... 29999999:
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return 3;
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case 30000000 ... 49999999:
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return 4;
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case 50000000 ... 79999999:
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return 5;
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case 80000000 ... 129999999:
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return 6;
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}
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return 7;
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}
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/**
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* __wrpll_calc_fbdiv() - return feedback fixed divide value
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* @c: ptr to a struct wrpll_cfg record to read from
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*
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* The internal feedback path includes a fixed by-two divider; the
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* external feedback path does not. Return the appropriate divider
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* value (2 or 1) depending on whether internal or external feedback
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* is enabled. This code doesn't test for invalid configurations
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* (e.g. both or neither of WRPLL_FLAGS_*_FEEDBACK are set); it relies
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* on the caller to do so.
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*
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* Context: Any context. Caller must protect the memory pointed to by
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* @c from simultaneous modification.
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*
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* Return: 2 if internal feedback is enabled or 1 if external feedback
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* is enabled.
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*/
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static u8 __wrpll_calc_fbdiv(const struct wrpll_cfg *c)
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{
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return (c->flags & WRPLL_FLAGS_INT_FEEDBACK_MASK) ? 2 : 1;
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}
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/**
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* __wrpll_calc_divq() - determine DIVQ based on target PLL output clock rate
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* @target_rate: target PLL output clock rate
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* @vco_rate: pointer to a u64 to store the computed VCO rate into
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*
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* Determine a reasonable value for the PLL Q post-divider, based on the
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* target output rate @target_rate for the PLL. Along with returning the
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* computed Q divider value as the return value, this function stores the
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* desired target VCO rate into the variable pointed to by @vco_rate.
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*
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* Context: Any context. Caller must protect the memory pointed to by
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* @vco_rate from simultaneous access or modification.
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*
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* Return: a positive integer DIVQ value to be programmed into the hardware
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* upon success, or 0 upon error (since 0 is an invalid DIVQ value)
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*/
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static u8 __wrpll_calc_divq(u32 target_rate, u64 *vco_rate)
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{
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u64 s;
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u8 divq = 0;
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if (!vco_rate) {
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WARN_ON(1);
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goto wcd_out;
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}
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s = div_u64(MAX_VCO_FREQ, target_rate);
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if (s <= 1) {
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divq = 1;
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*vco_rate = MAX_VCO_FREQ;
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} else if (s > MAX_DIVQ_DIVISOR) {
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divq = ilog2(MAX_DIVQ_DIVISOR);
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*vco_rate = MIN_VCO_FREQ;
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} else {
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divq = ilog2(s);
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*vco_rate = (u64)target_rate << divq;
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}
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wcd_out:
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return divq;
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}
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/**
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* __wrpll_update_parent_rate() - update PLL data when parent rate changes
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* @c: ptr to a struct wrpll_cfg record to write PLL data to
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* @parent_rate: PLL input refclk rate (pre-R-divider)
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*
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* Pre-compute some data used by the PLL configuration algorithm when
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* the PLL's reference clock rate changes. The intention is to avoid
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* computation when the parent rate remains constant - expected to be
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* the common case.
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*
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* Returns: 0 upon success or -ERANGE if the reference clock rate is
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* out of range.
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*/
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static int __wrpll_update_parent_rate(struct wrpll_cfg *c,
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unsigned long parent_rate)
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{
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u8 max_r_for_parent;
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if (parent_rate > MAX_INPUT_FREQ || parent_rate < MIN_POST_DIVR_FREQ)
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return -ERANGE;
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c->parent_rate = parent_rate;
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max_r_for_parent = div_u64(parent_rate, MIN_POST_DIVR_FREQ);
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c->max_r = min_t(u8, MAX_DIVR_DIVISOR, max_r_for_parent);
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c->init_r = DIV_ROUND_UP_ULL(parent_rate, MAX_POST_DIVR_FREQ);
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return 0;
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}
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/**
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* wrpll_configure() - compute PLL configuration for a target rate
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* @c: ptr to a struct wrpll_cfg record to write into
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* @target_rate: target PLL output clock rate (post-Q-divider)
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* @parent_rate: PLL input refclk rate (pre-R-divider)
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*
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* Compute the appropriate PLL signal configuration values and store
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* in PLL context @c. PLL reprogramming is not glitchless, so the
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* caller should switch any downstream logic to a different clock
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* source or clock-gate it before presenting these values to the PLL
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* configuration signals.
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*
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* The caller must pass this function a pre-initialized struct
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* wrpll_cfg record: either initialized to zero (with the
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* exception of the .name and .flags fields) or read from the PLL.
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*
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* Context: Any context. Caller must protect the memory pointed to by @c
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* from simultaneous access or modification.
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*
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* Return: 0 upon success; anything else upon failure.
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*/
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int wrpll_configure_for_rate(struct wrpll_cfg *c, u32 target_rate,
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unsigned long parent_rate)
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{
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unsigned long ratio;
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u64 target_vco_rate, delta, best_delta, f_pre_div, vco, vco_pre;
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u32 best_f, f, post_divr_freq;
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u8 fbdiv, divq, best_r, r;
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int range;
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if (c->flags == 0) {
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WARN(1, "%s called with uninitialized PLL config", __func__);
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return -EINVAL;
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}
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/* Initialize rounding data if it hasn't been initialized already */
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if (parent_rate != c->parent_rate) {
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if (__wrpll_update_parent_rate(c, parent_rate)) {
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pr_err("%s: PLL input rate is out of range\n",
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__func__);
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return -ERANGE;
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}
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}
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c->flags &= ~WRPLL_FLAGS_RESET_MASK;
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/* Put the PLL into bypass if the user requests the parent clock rate */
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if (target_rate == parent_rate) {
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c->flags |= WRPLL_FLAGS_BYPASS_MASK;
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return 0;
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}
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c->flags &= ~WRPLL_FLAGS_BYPASS_MASK;
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/* Calculate the Q shift and target VCO rate */
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divq = __wrpll_calc_divq(target_rate, &target_vco_rate);
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if (!divq)
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return -1;
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c->divq = divq;
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/* Precalculate the pre-Q divider target ratio */
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ratio = div64_u64((target_vco_rate << ROUND_SHIFT), parent_rate);
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fbdiv = __wrpll_calc_fbdiv(c);
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best_r = 0;
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best_f = 0;
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best_delta = MAX_VCO_FREQ;
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/*
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* Consider all values for R which land within
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* [MIN_POST_DIVR_FREQ, MAX_POST_DIVR_FREQ]; prefer smaller R
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*/
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for (r = c->init_r; r <= c->max_r; ++r) {
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f_pre_div = ratio * r;
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f = (f_pre_div + (1 << ROUND_SHIFT)) >> ROUND_SHIFT;
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f >>= (fbdiv - 1);
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post_divr_freq = div_u64(parent_rate, r);
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vco_pre = fbdiv * post_divr_freq;
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vco = vco_pre * f;
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/* Ensure rounding didn't take us out of range */
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if (vco > target_vco_rate) {
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--f;
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vco = vco_pre * f;
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} else if (vco < MIN_VCO_FREQ) {
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++f;
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vco = vco_pre * f;
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}
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delta = abs(target_rate - vco);
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if (delta < best_delta) {
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best_delta = delta;
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best_r = r;
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best_f = f;
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}
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}
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c->divr = best_r - 1;
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c->divf = best_f - 1;
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post_divr_freq = div_u64(parent_rate, best_r);
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/* Pick the best PLL jitter filter */
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range = __wrpll_calc_filter_range(post_divr_freq);
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if (range < 0)
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return range;
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c->range = range;
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return 0;
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}
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/**
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* wrpll_calc_output_rate() - calculate the PLL's target output rate
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* @c: ptr to a struct wrpll_cfg record to read from
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* @parent_rate: PLL refclk rate
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*
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* Given a pointer to the PLL's current input configuration @c and the
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* PLL's input reference clock rate @parent_rate (before the R
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* pre-divider), calculate the PLL's output clock rate (after the Q
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* post-divider).
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*
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* Context: Any context. Caller must protect the memory pointed to by @c
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* from simultaneous modification.
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*
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* Return: the PLL's output clock rate, in Hz. The return value from
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* this function is intended to be convenient to pass directly
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* to the Linux clock framework; thus there is no explicit
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* error return value.
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*/
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unsigned long wrpll_calc_output_rate(const struct wrpll_cfg *c,
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unsigned long parent_rate)
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{
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u8 fbdiv;
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u64 n;
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if (c->flags & WRPLL_FLAGS_EXT_FEEDBACK_MASK) {
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WARN(1, "external feedback mode not yet supported");
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return ULONG_MAX;
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}
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fbdiv = __wrpll_calc_fbdiv(c);
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n = parent_rate * fbdiv * (c->divf + 1);
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n = div_u64(n, c->divr + 1);
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n >>= c->divq;
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return n;
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}
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/**
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* wrpll_calc_max_lock_us() - return the time for the PLL to lock
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* @c: ptr to a struct wrpll_cfg record to read from
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*
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* Return the minimum amount of time (in microseconds) that the caller
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* must wait after reprogramming the PLL to ensure that it is locked
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* to the input frequency and stable. This is likely to depend on the DIVR
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* value; this is under discussion with the manufacturer.
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*
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* Return: the minimum amount of time the caller must wait for the PLL
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* to lock (in microseconds)
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*/
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unsigned int wrpll_calc_max_lock_us(const struct wrpll_cfg *c)
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{
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return MAX_LOCK_US;
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}
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