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v0.6.0
https://github.com/torvalds/linux
Tip revision: d5226fa6dbae0569ee43ecfc08bdcd6770fc4755 authored by Linus Torvalds on 27 January 2020, 00:23:03 UTC
Linux 5.5
Linux 5.5
Tip revision: d5226fa
wrpll-cln28hpc.c
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2018-2019 SiFive, Inc.
* Wesley Terpstra
* Paul Walmsley
*
* This library supports configuration parsing and reprogramming of
* the CLN28HPC variant of the Analog Bits Wide Range PLL. The
* intention is for this library to be reusable for any device that
* integrates this PLL; thus the register structure and programming
* details are expected to be provided by a separate IP block driver.
*
* The bulk of this code is primarily useful for clock configurations
* that must operate at arbitrary rates, as opposed to clock configurations
* that are restricted by software or manufacturer guidance to a small,
* pre-determined set of performance points.
*
* References:
* - Analog Bits "Wide Range PLL Datasheet", version 2015.10.01
* - SiFive FU540-C000 Manual v1p0, Chapter 7 "Clocking and Reset"
* https://static.dev.sifive.com/FU540-C000-v1.0.pdf
*/
#include <linux/bug.h>
#include <linux/err.h>
#include <linux/log2.h>
#include <linux/math64.h>
#include <linux/clk/analogbits-wrpll-cln28hpc.h>
/* MIN_INPUT_FREQ: minimum input clock frequency, in Hz (Fref_min) */
#define MIN_INPUT_FREQ 7000000
/* MAX_INPUT_FREQ: maximum input clock frequency, in Hz (Fref_max) */
#define MAX_INPUT_FREQ 600000000
/* MIN_POST_DIVIDE_REF_FREQ: minimum post-divider reference frequency, in Hz */
#define MIN_POST_DIVR_FREQ 7000000
/* MAX_POST_DIVIDE_REF_FREQ: maximum post-divider reference frequency, in Hz */
#define MAX_POST_DIVR_FREQ 200000000
/* MIN_VCO_FREQ: minimum VCO frequency, in Hz (Fvco_min) */
#define MIN_VCO_FREQ 2400000000UL
/* MAX_VCO_FREQ: maximum VCO frequency, in Hz (Fvco_max) */
#define MAX_VCO_FREQ 4800000000ULL
/* MAX_DIVQ_DIVISOR: maximum output divisor. Selected by DIVQ = 6 */
#define MAX_DIVQ_DIVISOR 64
/* MAX_DIVR_DIVISOR: maximum reference divisor. Selected by DIVR = 63 */
#define MAX_DIVR_DIVISOR 64
/* MAX_LOCK_US: maximum PLL lock time, in microseconds (tLOCK_max) */
#define MAX_LOCK_US 70
/*
* ROUND_SHIFT: number of bits to shift to avoid precision loss in the rounding
* algorithm
*/
#define ROUND_SHIFT 20
/*
* Private functions
*/
/**
* __wrpll_calc_filter_range() - determine PLL loop filter bandwidth
* @post_divr_freq: input clock rate after the R divider
*
* Select the value to be presented to the PLL RANGE input signals, based
* on the input clock frequency after the post-R-divider @post_divr_freq.
* This code follows the recommendations in the PLL datasheet for filter
* range selection.
*
* Return: The RANGE value to be presented to the PLL configuration inputs,
* or a negative return code upon error.
*/
static int __wrpll_calc_filter_range(unsigned long post_divr_freq)
{
if (post_divr_freq < MIN_POST_DIVR_FREQ ||
post_divr_freq > MAX_POST_DIVR_FREQ) {
WARN(1, "%s: post-divider reference freq out of range: %lu",
__func__, post_divr_freq);
return -ERANGE;
}
switch (post_divr_freq) {
case 0 ... 10999999:
return 1;
case 11000000 ... 17999999:
return 2;
case 18000000 ... 29999999:
return 3;
case 30000000 ... 49999999:
return 4;
case 50000000 ... 79999999:
return 5;
case 80000000 ... 129999999:
return 6;
}
return 7;
}
/**
* __wrpll_calc_fbdiv() - return feedback fixed divide value
* @c: ptr to a struct wrpll_cfg record to read from
*
* The internal feedback path includes a fixed by-two divider; the
* external feedback path does not. Return the appropriate divider
* value (2 or 1) depending on whether internal or external feedback
* is enabled. This code doesn't test for invalid configurations
* (e.g. both or neither of WRPLL_FLAGS_*_FEEDBACK are set); it relies
* on the caller to do so.
*
* Context: Any context. Caller must protect the memory pointed to by
* @c from simultaneous modification.
*
* Return: 2 if internal feedback is enabled or 1 if external feedback
* is enabled.
*/
static u8 __wrpll_calc_fbdiv(const struct wrpll_cfg *c)
{
return (c->flags & WRPLL_FLAGS_INT_FEEDBACK_MASK) ? 2 : 1;
}
/**
* __wrpll_calc_divq() - determine DIVQ based on target PLL output clock rate
* @target_rate: target PLL output clock rate
* @vco_rate: pointer to a u64 to store the computed VCO rate into
*
* Determine a reasonable value for the PLL Q post-divider, based on the
* target output rate @target_rate for the PLL. Along with returning the
* computed Q divider value as the return value, this function stores the
* desired target VCO rate into the variable pointed to by @vco_rate.
*
* Context: Any context. Caller must protect the memory pointed to by
* @vco_rate from simultaneous access or modification.
*
* Return: a positive integer DIVQ value to be programmed into the hardware
* upon success, or 0 upon error (since 0 is an invalid DIVQ value)
*/
static u8 __wrpll_calc_divq(u32 target_rate, u64 *vco_rate)
{
u64 s;
u8 divq = 0;
if (!vco_rate) {
WARN_ON(1);
goto wcd_out;
}
s = div_u64(MAX_VCO_FREQ, target_rate);
if (s <= 1) {
divq = 1;
*vco_rate = MAX_VCO_FREQ;
} else if (s > MAX_DIVQ_DIVISOR) {
divq = ilog2(MAX_DIVQ_DIVISOR);
*vco_rate = MIN_VCO_FREQ;
} else {
divq = ilog2(s);
*vco_rate = (u64)target_rate << divq;
}
wcd_out:
return divq;
}
/**
* __wrpll_update_parent_rate() - update PLL data when parent rate changes
* @c: ptr to a struct wrpll_cfg record to write PLL data to
* @parent_rate: PLL input refclk rate (pre-R-divider)
*
* Pre-compute some data used by the PLL configuration algorithm when
* the PLL's reference clock rate changes. The intention is to avoid
* computation when the parent rate remains constant - expected to be
* the common case.
*
* Returns: 0 upon success or -ERANGE if the reference clock rate is
* out of range.
*/
static int __wrpll_update_parent_rate(struct wrpll_cfg *c,
unsigned long parent_rate)
{
u8 max_r_for_parent;
if (parent_rate > MAX_INPUT_FREQ || parent_rate < MIN_POST_DIVR_FREQ)
return -ERANGE;
c->parent_rate = parent_rate;
max_r_for_parent = div_u64(parent_rate, MIN_POST_DIVR_FREQ);
c->max_r = min_t(u8, MAX_DIVR_DIVISOR, max_r_for_parent);
c->init_r = DIV_ROUND_UP_ULL(parent_rate, MAX_POST_DIVR_FREQ);
return 0;
}
/**
* wrpll_configure() - compute PLL configuration for a target rate
* @c: ptr to a struct wrpll_cfg record to write into
* @target_rate: target PLL output clock rate (post-Q-divider)
* @parent_rate: PLL input refclk rate (pre-R-divider)
*
* Compute the appropriate PLL signal configuration values and store
* in PLL context @c. PLL reprogramming is not glitchless, so the
* caller should switch any downstream logic to a different clock
* source or clock-gate it before presenting these values to the PLL
* configuration signals.
*
* The caller must pass this function a pre-initialized struct
* wrpll_cfg record: either initialized to zero (with the
* exception of the .name and .flags fields) or read from the PLL.
*
* Context: Any context. Caller must protect the memory pointed to by @c
* from simultaneous access or modification.
*
* Return: 0 upon success; anything else upon failure.
*/
int wrpll_configure_for_rate(struct wrpll_cfg *c, u32 target_rate,
unsigned long parent_rate)
{
unsigned long ratio;
u64 target_vco_rate, delta, best_delta, f_pre_div, vco, vco_pre;
u32 best_f, f, post_divr_freq;
u8 fbdiv, divq, best_r, r;
int range;
if (c->flags == 0) {
WARN(1, "%s called with uninitialized PLL config", __func__);
return -EINVAL;
}
/* Initialize rounding data if it hasn't been initialized already */
if (parent_rate != c->parent_rate) {
if (__wrpll_update_parent_rate(c, parent_rate)) {
pr_err("%s: PLL input rate is out of range\n",
__func__);
return -ERANGE;
}
}
c->flags &= ~WRPLL_FLAGS_RESET_MASK;
/* Put the PLL into bypass if the user requests the parent clock rate */
if (target_rate == parent_rate) {
c->flags |= WRPLL_FLAGS_BYPASS_MASK;
return 0;
}
c->flags &= ~WRPLL_FLAGS_BYPASS_MASK;
/* Calculate the Q shift and target VCO rate */
divq = __wrpll_calc_divq(target_rate, &target_vco_rate);
if (!divq)
return -1;
c->divq = divq;
/* Precalculate the pre-Q divider target ratio */
ratio = div64_u64((target_vco_rate << ROUND_SHIFT), parent_rate);
fbdiv = __wrpll_calc_fbdiv(c);
best_r = 0;
best_f = 0;
best_delta = MAX_VCO_FREQ;
/*
* Consider all values for R which land within
* [MIN_POST_DIVR_FREQ, MAX_POST_DIVR_FREQ]; prefer smaller R
*/
for (r = c->init_r; r <= c->max_r; ++r) {
f_pre_div = ratio * r;
f = (f_pre_div + (1 << ROUND_SHIFT)) >> ROUND_SHIFT;
f >>= (fbdiv - 1);
post_divr_freq = div_u64(parent_rate, r);
vco_pre = fbdiv * post_divr_freq;
vco = vco_pre * f;
/* Ensure rounding didn't take us out of range */
if (vco > target_vco_rate) {
--f;
vco = vco_pre * f;
} else if (vco < MIN_VCO_FREQ) {
++f;
vco = vco_pre * f;
}
delta = abs(target_rate - vco);
if (delta < best_delta) {
best_delta = delta;
best_r = r;
best_f = f;
}
}
c->divr = best_r - 1;
c->divf = best_f - 1;
post_divr_freq = div_u64(parent_rate, best_r);
/* Pick the best PLL jitter filter */
range = __wrpll_calc_filter_range(post_divr_freq);
if (range < 0)
return range;
c->range = range;
return 0;
}
/**
* wrpll_calc_output_rate() - calculate the PLL's target output rate
* @c: ptr to a struct wrpll_cfg record to read from
* @parent_rate: PLL refclk rate
*
* Given a pointer to the PLL's current input configuration @c and the
* PLL's input reference clock rate @parent_rate (before the R
* pre-divider), calculate the PLL's output clock rate (after the Q
* post-divider).
*
* Context: Any context. Caller must protect the memory pointed to by @c
* from simultaneous modification.
*
* Return: the PLL's output clock rate, in Hz. The return value from
* this function is intended to be convenient to pass directly
* to the Linux clock framework; thus there is no explicit
* error return value.
*/
unsigned long wrpll_calc_output_rate(const struct wrpll_cfg *c,
unsigned long parent_rate)
{
u8 fbdiv;
u64 n;
if (c->flags & WRPLL_FLAGS_EXT_FEEDBACK_MASK) {
WARN(1, "external feedback mode not yet supported");
return ULONG_MAX;
}
fbdiv = __wrpll_calc_fbdiv(c);
n = parent_rate * fbdiv * (c->divf + 1);
n = div_u64(n, c->divr + 1);
n >>= c->divq;
return n;
}
/**
* wrpll_calc_max_lock_us() - return the time for the PLL to lock
* @c: ptr to a struct wrpll_cfg record to read from
*
* Return the minimum amount of time (in microseconds) that the caller
* must wait after reprogramming the PLL to ensure that it is locked
* to the input frequency and stable. This is likely to depend on the DIVR
* value; this is under discussion with the manufacturer.
*
* Return: the minimum amount of time the caller must wait for the PLL
* to lock (in microseconds)
*/
unsigned int wrpll_calc_max_lock_us(const struct wrpll_cfg *c)
{
return MAX_LOCK_US;
}