[PATCH/RFC 3/3 v2] ARM: mach-shmobile: implement parent clock

[PATCH/RFC 3/3 v2] ARM: mach-shmobile: implement parent clock

[Guennadi Liakhovetski]

This new function allows to select a parent frequency, which provides the 
best matching child clock rate.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
---

Paul, something like this? I know, this is against an "old" kernel, only 
compile tested so far, so, this is even more of an RFC than the previous 
version, just to ask your opinion, if this is the direction you were 
thinking about. Unfortunately, I don't think re-using 
clk_rate_round_helper() would be wise here, but we can discuss that too. 

Thanks
Guennadi

diff --git a/drivers/sh/clk.c b/drivers/sh/clk.c
index 5d84ada..412620b 100644
--- a/drivers/sh/clk.c
+++ b/drivers/sh/clk.c
@@ -390,6 +390,79 @@ 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)) {
+			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;
+			}
+			if (!error)
+				break;
+			continue;
+		}
+
+		if (unlikely(freq->frequency >= target * div_max)) {
+			unsigned long freq_min = (freq->frequency + div_max / 2) / div_max;
+			if (error > target - freq_min) {
+				error = freq_min - target;
+				best = freq;
+				if (best_freq)
+					*best_freq = freq_min;
+			}
+			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 875ce50..d370057 100644
--- a/include/linux/sh_clk.h
+++ b/include/linux/sh_clk.h
@@ -111,6 +111,10 @@ int clk_rate_table_find(struct clk *clk,
 			struct cpufreq_frequency_table *freq_table,
 			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,					\

Re: [PATCH/RFC 3/3 v2] ARM: mach-shmobile: implement parent clock optimization

[Paul Mundt]

On Fri, Oct 29, 2010 at 02:42:16PM +0200, Guennadi Liakhovetski wrote:
> This new function allows to select a parent frequency, which provides the 
> best matching child clock rate.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> ---
> 
> Paul, something like this? I know, this is against an "old" kernel, only 
> compile tested so far, so, this is even more of an RFC than the previous 
> version, just to ask your opinion, if this is the direction you were 
> thinking about. Unfortunately, I don't think re-using 
> clk_rate_round_helper() would be wise here, but we can discuss that too. 
> 
Yes, that basically looks like what I had in mind. 

Re-using clk_rate_round_helper() probably won't help here since it's
doing sufficiently different things anyways.

If this ends up working for you then please test it and respin it against
a current kernel. This can go upstream pretty easily by itself.