On 25 November 2014 at 18:32, Mason <mpeg.blue@xxxxxxx> wrote:
> As far as I can tell, on my SoC, the timer runs at 27 MHz.
> But I have no idea how often it fires an interrupt.
27 MHz is the freq it runs at, but we get interrupt based on the value
programmed in the timer counter.
Look for CONFIG_HZ in your .config, that will tell you number of ticks
you are getting per second.
But cpufreq works in another level and so it doesn't depend on both
these.
Look for: /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
this is the rate at which cpufreq core checks if cpu's freq require revisiting.
> I've been studying other cpufreq drivers, especially the OMAP driver.
> I noticed that there is a lot of generic infrastructure that our driver
> wasn't using, such as...
>
> cpufreq_generic_init
> cpufreq_generic_exit
> cpufreq_generic_frequency_table_verify
> cpufreq_generic_attr
>
> I've changed our driver to use those.
Gud.
> I'm still confused about cpufreq_generic_get.
> This is not a typical get/put type function, right?
Correct, this should return the current frequency the CPU is running at.
> What is it supposed to get?
> Apparently, the actual frequency of the 'cpu-th' CPU?
> I see that it calls clk_get_rate(policy->clk)
Yes.
> This 'struct clk' is an elusive beast.
> Where is it defined? I only run into forward declarations.
Its architecture specific. What's the architecture you are working on?
You may implement your own routine instead of cpufreq_generic_get().
> On my platform, clk_get_accuracy returns -524 unconditionally,
That might be an error.
> and clk_prepare just returns 0.
>
> of_clk_get and of_clk_get_by_name both return ERR_PTR(-2)
>
> I suppose all this means I can't use this infrastructure "as-is",
> correct? Where can I read more about it?
Yes. Documentation/clk.txt.
> How is the kernel supposed to know what frequency each core is running at?
> I imagine that's what the .get method override is for?
Yeah. You should be able to get some call from your architecture.
> One more question (for now). Is the .get method supposed to return numbers
> that match in freq_table, or can they be slightly different? For example,
They should match.
> I've defined my freq_table like this:
>
> static struct cpufreq_frequency_table freq_table[] = {
> { .driver_data = REG_VAL(1,0), .frequency = 999000 },
> { .driver_data = REG_VAL(1,8), .frequency = 750000 },
> { .driver_data = REG_VAL(2,0), .frequency = 500000 },
> { .driver_data = REG_VAL(4,0), .frequency = 250000 },
> { .driver_data = REG_VAL(8,0), .frequency = 125000 },
> { .frequency = CPUFREQ_TABLE_END },
> };
>
> but the 3rd frequency is actually 999/2 MHz, not 500 MHz, etc.
> Will that be a problem?
Maybe, but it depends on what your ->get() returns.
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