cpufreq: frequency scaling spec in DT node

On 29/06/2017 16:34, Viresh Kumar wrote:

On 29-06-17, 13:41, Mason wrote:

quoted

I was trying to "emulate" the behavior of the ondemand governor.
Based on your reaction, I got it wrong...
Here is the actual issue:

I'm on SoC B, where nominal/max freq is expected to be 1206 MHz.
So the OPPs in the DT are:
operating-points = <1206000 0 603000 0 402000 0 241200 0 134000 0>;
*But* FW changed the max freq behind my back, to 1215 MHz.

Here is what happens when I execute:
echo ondemand >scaling_governor
sleep 2
cpuburn-a9 & cpuburn-a9 & cpuburn-a9 & cpuburn-a9
### cpuburn-a9 spins in a tight infinite loop,
### hitting all FUs to raise the CPU temperature

# cpufreq_test.sh
[   69.933874] set_target: index=4
[   69.944799] set_target: index=2
[   69.947988] clk_divider_set_rate: rate=303750000 parent_rate=1215000000 div=4
[   69.955542] set_target: index=4
[   69.958801] clk_divider_set_rate: rate=607500000 parent_rate=1215000000 div=2
[   69.984789] set_target: index=0
[   69.987980] clk_divider_set_rate: rate=121500000 parent_rate=1215000000 div=10
[   71.947597] set_target: index=4
[   71.950996] clk_divider_set_rate: rate=607500000 parent_rate=1215000000 div=2

As you can see, the divider remains stuck at 2, so the SoC
is actually running only at 607.5 MHz (instead of 1215 MHz).

If I fix the OPPs in DT to:
operating-points = <1215000 0 607500 0 405000 0 243000 0 135000 0>;
Then I get the expected behavior:

$ cpufreq_test.sh 
[   32.717930] set_target: index=1
[   32.721131] clk_divider_set_rate: rate=243000000 parent_rate=1215000000 div=5
[   32.731326] set_target: index=4
[   32.734521] clk_divider_set_rate: rate=1215000000 parent_rate=1215000000 div=1
[   32.754556] set_target: index=0
[   32.757738] clk_divider_set_rate: rate=135000000 parent_rate=1215000000 div=9
[   32.765864] set_target: index=4
[   32.769217] clk_divider_set_rate: rate=1215000000 parent_rate=1215000000 div=1
[   33.438811] set_target: index=0
[   33.442001] clk_divider_set_rate: rate=135000000 parent_rate=1215000000 div=9
[   33.450249] set_target: index=4
[   33.453470] clk_divider_set_rate: rate=1215000000 parent_rate=1215000000 div=1
[   33.477888] set_target: index=0
[   33.481067] clk_divider_set_rate: rate=135000000 parent_rate=1215000000 div=9
[   34.714786] set_target: index=4
[   34.718237] clk_divider_set_rate: rate=1215000000 parent_rate=1215000000 div=1

Divider settles at 1 (full speed) to provide maximum
performance for the user-space processes.

I am not sure how such behavior will happen just because we changed
the max OPP (actually increased it). You need to dig in a bit to see
why this happens, as I can't agree to your numbers for now.

I had a closer look.

static int _div_round(...)
{
	if (flags & CLK_DIVIDER_ROUND_CLOSEST)
		return _div_round_closest(table, parent_rate, rate, flags);

	return _div_round_up(table, parent_rate, rate, flags);
}

This flag was /not/ set for the CPU divider clock.
But setting it breaks in dev_pm_opp_set_rate()

[    9.201681] set_target: index=4
[    9.204870] dev_pm_opp_set_rate: target_freq=1206000000 freq=1215000000 old_freq=243000000
[    9.213647] cpu cpu0: dev_pm_opp_set_rate: failed to find OPP for freq 1215000000 (-34)
[    9.222029] cpufreq: __target_index: Failed to change cpu frequency: -34



I'll experiment with the other solution of creating the OPP table
at init.

Regards.