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sh: add clk_round_parent() to optimize parent clock rate 

Sometimes it is possible and reasonable to adjust the parent clock rate to
improve precision of the child clock, e.g., if the child clock has no siblings.
clk_round_parent() is a new addition to the SH clock-framework API, that
implements such an optimization for child clocks with divisors, taking all
integer values in a range.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
This commit is contained in:
Guennadi Liakhovetski 2010-11-02 11:27:24 +00:00 committed by Paul Mundt
parent 5aefa34fad
commit 6af26c6c99
2 changed files with 79 additions and 0 deletions
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75
drivers/sh/clk/core.c
View File

@ -541,6 +541,81 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
}
EXPORT_SYMBOL_GPL(clk_round_rate);
long clk_round_parent(struct clk *clk, unsigned long target,
unsigned long *best_freq, unsigned long *parent_freq,
unsigned int div_min, unsigned int div_max)
{
struct cpufreq_frequency_table *freq, *best = NULL;
unsigned long error = ULONG_MAX, freq_high, freq_low, div;
struct clk *parent = clk_get_parent(clk);
if (!parent) {
*parent_freq = 0;
*best_freq = clk_round_rate(clk, target);
return abs(target - *best_freq);
}
for (freq = parent->freq_table; freq->frequency != CPUFREQ_TABLE_END;
freq++) {
if (freq->frequency == CPUFREQ_ENTRY_INVALID)
continue;
if (unlikely(freq->frequency / target <= div_min - 1)) {
unsigned long freq_max = (freq->frequency + div_min / 2) / div_min;
if (error > target - freq_max) {
error = target - freq_max;
best = freq;
if (best_freq)
*best_freq = freq_max;
}
pr_debug("too low freq %lu, error %lu\n", freq->frequency, target - freq_max);
if (!error)
break;
continue;
}
if (unlikely(freq->frequency / target >= div_max)) {
unsigned long freq_min = (freq->frequency + div_max / 2) / div_max;
if (error > freq_min - target) {
error = freq_min - target;
best = freq;
if (best_freq)
*best_freq = freq_min;
}
pr_debug("too high freq %lu, error %lu\n", freq->frequency, freq_min - target);
if (!error)
break;
continue;
}
div = freq->frequency / target;
freq_high = freq->frequency / div;
freq_low = freq->frequency / (div + 1);
if (freq_high - target < error) {
error = freq_high - target;
best = freq;
if (best_freq)
*best_freq = freq_high;
}
if (target - freq_low < error) {
error = target - freq_low;
best = freq;
if (best_freq)
*best_freq = freq_low;
}
pr_debug("%u / %lu = %lu, / %lu = %lu, best %lu, parent %u\n",
freq->frequency, div, freq_high, div + 1, freq_low,
*best_freq, best->frequency);
if (!error)
break;
}
if (parent_freq)
*parent_freq = best->frequency;
return error;
}
EXPORT_SYMBOL_GPL(clk_round_parent);
#ifdef CONFIG_PM
static int clks_sysdev_suspend(struct sys_device *dev, pm_message_t state)
{

4
include/linux/sh_clk.h
View File

@ -122,6 +122,10 @@ int clk_rate_table_find(struct clk *clk,
long clk_rate_div_range_round(struct clk *clk, unsigned int div_min,
unsigned int div_max, unsigned long rate);
long clk_round_parent(struct clk *clk, unsigned long target,
unsigned long *best_freq, unsigned long *parent_freq,
unsigned int div_min, unsigned int div_max);
#define SH_CLK_MSTP32(_parent, _enable_reg, _enable_bit, _flags) \
{ \
.parent = _parent, \