cpufreq: CPPC: Enable fast_switch

The communication mean of the _CPC desired performance can be
PCC, System Memory, System IO, or Functional Fixed Hardware.

commit b7898fda5bc7 ("cpufreq: Support for fast frequency switching")
fast_switching is 'for switching CPU frequencies from interrupt
context'.
Writes to SystemMemory and SystemIo are fast and suitable this.
This is not the case for PCC and might not be the case for FFH.

Enable fast_switching for the cppc_cpufreq driver in above cases.

Add cppc_allow_fast_switch() to check the desired performance
register address space and set fast_switching accordingly.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 840223c12540..3b299b28a8af 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -434,6 +434,24 @@ bool acpi_cpc_valid(void)
 }
 EXPORT_SYMBOL_GPL(acpi_cpc_valid);
 
+bool cppc_allow_fast_switch(void)
+{
+	struct cpc_register_resource *desired_reg;
+	struct cpc_desc *cpc_ptr;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		cpc_ptr = per_cpu(cpc_desc_ptr, cpu);
+		desired_reg = &cpc_ptr->cpc_regs[DESIRED_PERF];
+		if (!CPC_IN_SYSTEM_MEMORY(desired_reg) &&
+				!CPC_IN_SYSTEM_IO(desired_reg))
+			return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(cppc_allow_fast_switch);
+
 /**
  * acpi_get_psd_map - Map the CPUs in the freq domain of a given cpu
  * @cpu: Find all CPUs that share a domain with cpu.