acpi-cpufreq: Add comment under ACPI_ADR_SPACE_SYSTEM_IO case

policy->cur is now set by cpufreq core when cpufreq_driver->get() is defined and
so drivers aren't required to set it. When space_id is ACPI_ADR_SPACE_SYSTEM_IO
for acpi cpufreq driver it doesn't set ->get to a valid function pointer and so
policy->cur is required to be set by driver.

This is already followed in acpi-cpufreq driver. This patch adds a comment
describing why we need to set policy->cur from driver.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index a8dac7b..a1717d7 100644 (file)
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -837,7 +837,12 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
        switch (perf->control_register.space_id) {
        case ACPI_ADR_SPACE_SYSTEM_IO:
-               /* Current speed is unknown and not detectable by IO port */
+               /*
+                * The core will not set policy->cur, because
+                * cpufreq_driver->get is NULL, so we need to set it here.
+                * However, we have to guess it, because the current speed is
+                * unknown and not detectable via IO ports.
+                */
                policy->cur = acpi_cpufreq_guess_freq(data, policy->cpu);
                break;
        case ACPI_ADR_SPACE_FIXED_HARDWARE: