On 10/23/2012 11:30 AM, Andrew Lunn wrote:

On Tue, Oct 23, 2012 at 11:11:53AM +0200, Gregory CLEMENT wrote:

quoted

On 10/22/2012 08:45 PM, Andrew Lunn wrote:

quoted

Hi Gregory

quoted

+void __init set_secondary_cpus_clock(void)
+{
+	int cpu;
+	unsigned long rate;
+	struct clk *cpu_clk = NULL;
+	struct device_node *np = NULL;
+
+	cpu = smp_processor_id();
+	np = of_find_node_by_type(np, "cpu");
+	np = NULL;
+	while ((np = of_find_node_by_type(np, "cpu"))) {
+		const u32 *reg;
+		int len;
+		reg = of_get_property(np, "reg", &len);
+		if (!reg || len != 4) {
+			pr_err("%s missing reg property\n", np->full_name);
+			continue;
+		}
+		if (be32_to_cpup(reg) == cpu) {
+			cpu_clk = of_clk_get(np, 0);
+			break;
+		}
+	}
+	WARN_ON(IS_ERR(cpu_clk));
+	rate = clk_get_rate(cpu_clk);
+
+	/* set all the other CPU clk to the same rate than the boot CPU */
+	np = NULL;
+	while ((np = of_find_node_by_type(np, "cpu"))) {
+		const u32 *reg;
+		int len;
+		reg = of_get_property(np, "reg", &len);
+		if (!reg || len != 4) {
+			pr_err("%s missing reg property\n", np->full_name);
+			continue;
+		}
+		if (be32_to_cpup(reg) != cpu) {
+			cpu_clk = of_clk_get(np, 0);
+			clk_set_rate(cpu_clk, rate);
+		}

Maybe its hiding somewhere, but where is the clk_prepare_enable() for
this cpu_clk clock?

Well the clocks are always enable. In the clock framework, the cpu clocks
don't provide an enable function.

Is it possible in the hardware to disable them? Turning them off might
save some power. If these chips end up in some data center server, it
might be that CPU hotplugging is used.

Well I didn't find anything about it. You can power off a CPU using the
PMSU but not the clock itself. I guess that once you have power off the
CPU the clock will be turned off as well.

quoted

But maybe it is cleaner to call clk_prepare_enable() even if it does
nothing except update the usage count.

You also have to watch out for the late_initcall which will disable
all clocks which are running but nobody has claimed. This will become
an issue if you do have enable/disable function in later versions of
the clock functions.

I don't think there will be enable/disable functions for the family
clock currently used (armada-xp-cpu-clockctrl). But in future if a new
version of mvebu SoC will use a new clock family which will have these
functions, then it will be an issue. So to be future proof I will ad
this call in the next version of the patch set.

	Andrew

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com