Re: [PATCH 1/6] cpufreq: cpufreq-cpu0: allow optional safe voltage during frequency transitions

Shawn Guo
2014-01-13T03:13:44Z

Hi Thomas,

On Thu, Jan 09, 2014 at 09:29:20PM +0530, Thomas Abraham wrote:
> @@ -19,6 +19,10 @@ Optional properties:
> - cooling-min-level:
> - cooling-max-level:
> Please refer to Documentation/devicetree/bindings/thermal/thermal.txt.
> +- safe-opp-index: Certain platforms require that during a opp transition,
> + a system should not go below a particular opp level. For such systems,
> + this property specifies the minimum opp to be maintained during the
> + opp transitions.

<snip>

> @@ -165,13 +196,27 @@ static int cpu0_cpufreq_probe(struct platform_device *pdev)
> goto out_put_node;
> }
>
> + if (!of_property_read_u32(np, "safe-opp-index", &safe_opp_index)) {
> + rcu_read_lock();
> + opp = dev_pm_opp_find_freq_exact(cpu_dev,
> + freq_table[safe_opp_index].frequency * 1000, true);

The property safe_opp_index is directly used to index freq_table here.
It only works when the opp table in device tree is defined in increasing
order. But we have nothing in opp binding bindings/power/opp.txt to
enforce it. That said, opp table in device tree could be in arbitrary
order, and thus safe_opp_index gives you nothing reliable.

Shawn

> + if (IS_ERR(opp)) {
> + rcu_read_unlock();
> + pr_err("safe opp index %d is invalid\n",
> + safe_opp_index);
> + goto out_free_table;
> + }
> + safe_voltage = dev_pm_opp_get_voltage(opp);
> + safe_frequency = freq_table[safe_opp_index].frequency;
> + rcu_read_unlock();
> + }
> +
> of_property_read_u32(np, "voltage-tolerance", &voltage_tolerance);
>
> if (of_property_read_u32(np, "clock-latency", &transition_latency))
> transition_latency = CPUFREQ_ETERNAL;
>
> if (!IS_ERR(cpu_reg)) {
> - struct dev_pm_opp *opp;
> unsigned long min_uV, max_uV;
> int i;
>
> --
> 1.6.6.rc2
>