Hi Thomas,
> 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.
Please look into my comments about reparenting at PATCH 3/6.
>
> 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@xxxxxxxxxx>
> Signed-off-by: Thomas Abraham <thomas.ab@xxxxxxxxxxx>
> ---
> .../devicetree/bindings/cpufreq/cpufreq-cpu0.txt | 5 ++
> drivers/cpufreq/cpufreq-cpu0.c | 49
> +++++++++++++++++++- 2 files changed, 52 insertions(+), 2 deletions(-)
>
> diff --git
> a/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt
> b/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt index
> f055515..020d859 100644 ---
> a/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt +++
> b/Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt @@ -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.
>
> Examples:
>
> @@ -36,6 +40,7 @@ cpus {
> 396000 950000
> 198000 850000
> >;
> + safe-opp-index = <1>;
> 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..dda4b7b 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;
> @@ -69,12 +71,26 @@ static int cpu0_set_target(struct cpufreq_policy
> *policy, unsigned int index) 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(cpu_reg, safe_voltage,
> + safe_voltage);
> + if (ret) {
> + pr_err("failed to set safe voltage: %d\n",
> ret);
> + return ret;
> + }
> }
>
> ret = clk_set_rate(cpu_clk, freq_exact);
> @@ -94,6 +110,19 @@ static int cpu0_set_target(struct cpufreq_policy
> *policy, unsigned int index) }
> }
>
> + /*
> + * if safe voltage was applied during voltage scale up, then
> set
> + * the correct target voltage now.
> + */
> + 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;
> + }
> + }
> +
> return ret;
> }
>
> @@ -116,7 +145,9 @@ static struct cpufreq_driver cpu0_cpufreq_driver
> = {
> static int cpu0_cpufreq_probe(struct platform_device *pdev)
> {
> + struct dev_pm_opp *opp;
> struct device_node *np;
> + unsigned int safe_opp_index;
> int ret;
>
> cpu_dev = get_cpu_device(0);
> @@ -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);
> + 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;
>
Reviewed-by: Lukasz Majewski <l.majewski@xxxxxxxxxxx>
--
Best regards,
Lukasz Majewski
Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
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