linux/drivers/clk/clk-fractional-divider.c
Frank Oltmanns 2e9abc6ec1 clk: fractional-divider: Improve approximation when zero based and export
Consider the CLK_FRAC_DIVIDER_ZERO_BASED flag when finding the best
approximation for m and n. By doing so, increase the range of valid
values for the numerator and denominator by 1.

Furthermore, export the approximation function so that users of this
function can be compiled as modules.

Cc: A.s. Dong <aisheng.dong@nxp.com>
Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Link: https://lore.kernel.org/r/20230617131041.18313-2-frank@oltmanns.dev
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
2023-10-12 14:02:17 -07:00

326 lines
7.9 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2014 Intel Corporation
*
* Adjustable fractional divider clock implementation.
* Uses rational best approximation algorithm.
*
* Output is calculated as
*
* rate = (m / n) * parent_rate (1)
*
* This is useful when we have a prescaler block which asks for
* m (numerator) and n (denominator) values to be provided to satisfy
* the (1) as much as possible.
*
* Since m and n have the limitation by a range, e.g.
*
* n >= 1, n < N_width, where N_width = 2^nwidth (2)
*
* for some cases the output may be saturated. Hence, from (1) and (2),
* assuming the worst case when m = 1, the inequality
*
* floor(log2(parent_rate / rate)) <= nwidth (3)
*
* may be derived. Thus, in cases when
*
* (parent_rate / rate) >> N_width (4)
*
* we might scale up the rate by 2^scale (see the description of
* CLK_FRAC_DIVIDER_POWER_OF_TWO_PS for additional information), where
*
* scale = floor(log2(parent_rate / rate)) - nwidth (5)
*
* and assume that the IP, that needs m and n, has also its own
* prescaler, which is capable to divide by 2^scale. In this way
* we get the denominator to satisfy the desired range (2) and
* at the same time a much better result of m and n than simple
* saturated values.
*/
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/io.h>
#include <linux/math.h>
#include <linux/module.h>
#include <linux/rational.h>
#include <linux/slab.h>
#include <linux/clk-provider.h>
#include "clk-fractional-divider.h"
static inline u32 clk_fd_readl(struct clk_fractional_divider *fd)
{
if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
return ioread32be(fd->reg);
return readl(fd->reg);
}
static inline void clk_fd_writel(struct clk_fractional_divider *fd, u32 val)
{
if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
iowrite32be(val, fd->reg);
else
writel(val, fd->reg);
}
static void clk_fd_get_div(struct clk_hw *hw, struct u32_fract *fract)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long flags = 0;
unsigned long m, n;
u32 mmask, nmask;
u32 val;
if (fd->lock)
spin_lock_irqsave(fd->lock, flags);
else
__acquire(fd->lock);
val = clk_fd_readl(fd);
if (fd->lock)
spin_unlock_irqrestore(fd->lock, flags);
else
__release(fd->lock);
mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
m = (val & mmask) >> fd->mshift;
n = (val & nmask) >> fd->nshift;
if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
m++;
n++;
}
fract->numerator = m;
fract->denominator = n;
}
static unsigned long clk_fd_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
{
struct u32_fract fract;
u64 ret;
clk_fd_get_div(hw, &fract);
if (!fract.numerator || !fract.denominator)
return parent_rate;
ret = (u64)parent_rate * fract.numerator;
do_div(ret, fract.denominator);
return ret;
}
void clk_fractional_divider_general_approximation(struct clk_hw *hw,
unsigned long rate,
unsigned long *parent_rate,
unsigned long *m, unsigned long *n)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long max_m, max_n;
/*
* Get rate closer to *parent_rate to guarantee there is no overflow
* for m and n. In the result it will be the nearest rate left shifted
* by (scale - fd->nwidth) bits.
*
* For the detailed explanation see the top comment in this file.
*/
if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) {
unsigned long scale = fls_long(*parent_rate / rate - 1);
if (scale > fd->nwidth)
rate <<= scale - fd->nwidth;
}
if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
max_m = 1 << fd->mwidth;
max_n = 1 << fd->nwidth;
} else {
max_m = GENMASK(fd->mwidth - 1, 0);
max_n = GENMASK(fd->nwidth - 1, 0);
}
rational_best_approximation(rate, *parent_rate, max_m, max_n, m, n);
}
EXPORT_SYMBOL_GPL(clk_fractional_divider_general_approximation);
static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
unsigned long *parent_rate)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long m, n;
u64 ret;
if (!rate || (!clk_hw_can_set_rate_parent(hw) && rate >= *parent_rate))
return *parent_rate;
if (fd->approximation)
fd->approximation(hw, rate, parent_rate, &m, &n);
else
clk_fractional_divider_general_approximation(hw, rate, parent_rate, &m, &n);
ret = (u64)*parent_rate * m;
do_div(ret, n);
return ret;
}
static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
unsigned long parent_rate)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long flags = 0;
unsigned long m, n, max_m, max_n;
u32 mmask, nmask;
u32 val;
if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
max_m = 1 << fd->mwidth;
max_n = 1 << fd->nwidth;
} else {
max_m = GENMASK(fd->mwidth - 1, 0);
max_n = GENMASK(fd->nwidth - 1, 0);
}
rational_best_approximation(rate, parent_rate, max_m, max_n, &m, &n);
if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
m--;
n--;
}
if (fd->lock)
spin_lock_irqsave(fd->lock, flags);
else
__acquire(fd->lock);
mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
val = clk_fd_readl(fd);
val &= ~(mmask | nmask);
val |= (m << fd->mshift) | (n << fd->nshift);
clk_fd_writel(fd, val);
if (fd->lock)
spin_unlock_irqrestore(fd->lock, flags);
else
__release(fd->lock);
return 0;
}
#ifdef CONFIG_DEBUG_FS
static int clk_fd_numerator_get(void *hw, u64 *val)
{
struct u32_fract fract;
clk_fd_get_div(hw, &fract);
*val = fract.numerator;
return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_numerator_fops, clk_fd_numerator_get, NULL, "%llu\n");
static int clk_fd_denominator_get(void *hw, u64 *val)
{
struct u32_fract fract;
clk_fd_get_div(hw, &fract);
*val = fract.denominator;
return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_denominator_fops, clk_fd_denominator_get, NULL, "%llu\n");
static void clk_fd_debug_init(struct clk_hw *hw, struct dentry *dentry)
{
debugfs_create_file("numerator", 0444, dentry, hw, &clk_fd_numerator_fops);
debugfs_create_file("denominator", 0444, dentry, hw, &clk_fd_denominator_fops);
}
#endif
const struct clk_ops clk_fractional_divider_ops = {
.recalc_rate = clk_fd_recalc_rate,
.round_rate = clk_fd_round_rate,
.set_rate = clk_fd_set_rate,
#ifdef CONFIG_DEBUG_FS
.debug_init = clk_fd_debug_init,
#endif
};
EXPORT_SYMBOL_GPL(clk_fractional_divider_ops);
struct clk_hw *clk_hw_register_fractional_divider(struct device *dev,
const char *name, const char *parent_name, unsigned long flags,
void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
u8 clk_divider_flags, spinlock_t *lock)
{
struct clk_fractional_divider *fd;
struct clk_init_data init;
struct clk_hw *hw;
int ret;
fd = kzalloc(sizeof(*fd), GFP_KERNEL);
if (!fd)
return ERR_PTR(-ENOMEM);
init.name = name;
init.ops = &clk_fractional_divider_ops;
init.flags = flags;
init.parent_names = parent_name ? &parent_name : NULL;
init.num_parents = parent_name ? 1 : 0;
fd->reg = reg;
fd->mshift = mshift;
fd->mwidth = mwidth;
fd->nshift = nshift;
fd->nwidth = nwidth;
fd->flags = clk_divider_flags;
fd->lock = lock;
fd->hw.init = &init;
hw = &fd->hw;
ret = clk_hw_register(dev, hw);
if (ret) {
kfree(fd);
hw = ERR_PTR(ret);
}
return hw;
}
EXPORT_SYMBOL_GPL(clk_hw_register_fractional_divider);
struct clk *clk_register_fractional_divider(struct device *dev,
const char *name, const char *parent_name, unsigned long flags,
void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
u8 clk_divider_flags, spinlock_t *lock)
{
struct clk_hw *hw;
hw = clk_hw_register_fractional_divider(dev, name, parent_name, flags,
reg, mshift, mwidth, nshift, nwidth, clk_divider_flags,
lock);
if (IS_ERR(hw))
return ERR_CAST(hw);
return hw->clk;
}
EXPORT_SYMBOL_GPL(clk_register_fractional_divider);
void clk_hw_unregister_fractional_divider(struct clk_hw *hw)
{
struct clk_fractional_divider *fd;
fd = to_clk_fd(hw);
clk_hw_unregister(hw);
kfree(fd);
}