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>

diff --git a/drivers/sh/clk/core.c b/drivers/sh/clk/core.c
index 861144360d8930587baa27d2303d21523e2581de..b3840597ad6efddf2042eecd01d60ff1b7aca18c 100644 (file)
--- a/drivers/sh/clk/core.c
+++ b/drivers/sh/clk/core.c
@@ -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)
 {

diff --git a/include/linux/sh_clk.h b/include/linux/sh_clk.h
index 4dca992f3093771993ac9d98d1233df5e2f33cfa..cea0c38e7a63dfad2544043c49fca25aea9a7563 100644 (file)
--- a/include/linux/sh_clk.h
+++ b/include/linux/sh_clk.h
@@ -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,                                      \