Re: [PATCH v2 1/7] cpufreq: cpufreq-cpu0: allow optional safe voltage during frequency transitions

Thomas Abraham
2014-01-28T04:30:47Z

Hi Shawn,

On Mon, Jan 27, 2014 at 12:46 PM, Shawn Guo <shawn.guo@linaro.org> wrote:
> On Sat, Jan 18, 2014 at 05:40:51PM +0530, Thomas Abraham wrote:
>> From: Thomas Abraham <thomas.ab@samsung.com>
>>
>> On some platforms such as the Samsung Exynos, changing the frequency
>> of the CPU clock requires changing the frequency of the PLL that is
>> supplying the CPU clock. To change the frequency of the PLL, the CPU
>> clock is temporarily reparented to another parent clock.
>>
>> The clock frequency of this temporary parent clock could be much higher
>> than the clock frequency of the PLL at the time of reparenting. Due
>> to the temporary increase in the CPU clock speed, the CPU (and any other
>> components in the CPU clock domain such as dividers, mux, etc.) have to
>> to be operated at a higher voltage level, called the safe voltage level.
>> This patch adds optional support to temporarily switch to a safe voltage
>> level during CPU frequency transitions.
>>
>> Cc: Shawn Guo <shawn.guo@linaro.org>
>> Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
>> ---
>> .../devicetree/bindings/cpufreq/cpufreq-cpu0.txt | 7 ++++
>
> The devicetree list should be copied for this change.

Okay, will do in the next version.

>
>> drivers/cpufreq/cpufreq-cpu0.c | 37 +++++++++++++++++--
>> 2 files changed, 40 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt b/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt
>> index f055515..37453ab 100644
>> --- a/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt
>> +++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt
>> @@ -19,6 +19,12 @@ Optional properties:
>> - cooling-min-level:
>> - cooling-max-level:
>> Please refer to Documentation/devicetree/bindings/thermal/thermal.txt.
>> +- safe-opp: 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. The safe-opp value is a tuple with first element
>> + representing the safe frequency and the second element representing the
>> + safe voltage.
>>
>> Examples:
>>
>> @@ -36,6 +42,7 @@ cpus {
>> 396000 950000
>> 198000 850000
>> >;
>> + safe-opp = <396000 950000>
>> clock-latency = <61036>; /* two CLK32 periods */
>> #cooling-cells = <2>;
>> cooling-min-level = <0>;
>> diff --git a/drivers/cpufreq/cpufreq-cpu0.c b/drivers/cpufreq/cpufreq-cpu0.c
>> index 0c12ffc..075d3d1 100644
>> --- a/drivers/cpufreq/cpufreq-cpu0.c
>> +++ b/drivers/cpufreq/cpufreq-cpu0.c
>> @@ -27,6 +27,8 @@
>>
>> static unsigned int transition_latency;
>> static unsigned int voltage_tolerance; /* in percentage */
>> +static unsigned long safe_frequency;
>> +static unsigned long safe_voltage;
>>
>> static struct device *cpu_dev;
>> static struct clk *cpu_clk;
>> @@ -64,17 +66,30 @@ static int cpu0_set_target(struct cpufreq_policy *policy, unsigned int index)
>> volt_old = regulator_get_voltage(cpu_reg);
>> }
>>
>> - pr_debug("%u MHz, %ld mV --> %u MHz, %ld mV\n",
>> + pr_debug("\n\n%u MHz, %ld mV --> %u MHz, %ld mV\n",
>
> This is an unnecessary change?

Yes, sorry missed that.

>
> Otherwise,
>
> Acked-by: Shawn Guo <shawn.guo@linaro.org>

Thanks for your review.

Regards,
Thomas.

>
> Shawn
>
>> old_freq / 1000, volt_old ? volt_old / 1000 : -1,
>> new_freq / 1000, volt ? volt / 1000 : -1);
>>
>> /* scaling up? scale voltage before frequency */
>> - if (!IS_ERR(cpu_reg) && new_freq > old_freq) {
>> + if (!IS_ERR(cpu_reg) && new_freq > old_freq &&
>> + new_freq >= safe_frequency) {
>> ret = regulator_set_voltage_tol(cpu_reg, volt, tol);
>> if (ret) {
>> pr_err("failed to scale voltage up: %d\n", ret);
>> return ret;
>> }
>> + } else if (!IS_ERR(cpu_reg) && old_freq < safe_frequency) {
>> + /*
>> + * the scaled up voltage level for the new_freq is lower
>> + * than the safe voltage level. so set safe_voltage
>> + * as the intermediate voltage level and revert it
>> + * back after the frequency has been changed.
>> + */
>> + ret = regulator_set_voltage_tol(cpu_reg, safe_voltage, tol);
>> + if (ret) {
>> + pr_err("failed to set safe voltage: %d\n", ret);
>> + return ret;
>> + }
>> }
>>
>> ret = clk_set_rate(cpu_clk, freq_exact);
>> @@ -86,7 +101,8 @@ static int cpu0_set_target(struct cpufreq_policy *policy, unsigned int index)
>> }
>>
>> /* scaling down? scale voltage after frequency */
>> - if (!IS_ERR(cpu_reg) && new_freq < old_freq) {
>> + if (!IS_ERR(cpu_reg) &&
>> + (new_freq < old_freq || new_freq < safe_frequency)) {
>> ret = regulator_set_voltage_tol(cpu_reg, volt, tol);
>> if (ret) {
>> pr_err("failed to scale voltage down: %d\n", ret);
>> @@ -116,6 +132,8 @@ static struct cpufreq_driver cpu0_cpufreq_driver = {
>>
>> static int cpu0_cpufreq_probe(struct platform_device *pdev)
>> {
>> + const struct property *prop;
>> + struct dev_pm_opp *opp;
>> struct device_node *np;
>> int ret;
>>
>> @@ -165,13 +183,24 @@ static int cpu0_cpufreq_probe(struct platform_device *pdev)
>> goto out_put_node;
>> }
>>
>> + prop = of_find_property(np, "safe-opp", NULL);
>> + if (prop) {
>> + if (prop->value && (prop->length / sizeof(u32)) == 2) {
>> + const __be32 *val;
>> + val = prop->value;
>> + safe_frequency = be32_to_cpup(val++);
>> + safe_voltage = be32_to_cpup(val);
>> + } else {
>> + pr_err("invalid safe-opp level specified\n");
>> + }
>> + }
>> +
>> 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
>>
>