Commit a755d0e2 authored by Qais Yousef's avatar Qais Yousef Committed by Rafael J. Wysocki
Browse files

cpufreq: Honour transition_latency over transition_delay_us 



Some platforms like Arm's Juno can have a high transition latency that
can be larger than the 2ms cap introduced. If a driver reports
a transition_latency that is higher than the cap, then use it as-is.

Update comment s/10/2/ to reflect the new cap of 2ms.

Reported-by: default avatarPierre Gondois <pierre.gondois@arm.com>
Signed-off-by: default avatarQais Yousef <qyousef@layalina.io>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent d394abcb

drivers/cpufreq/cpufreq.c

+11 −2
Original line number Diff line number Diff line
@@ -576,8 +576,17 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy) 


	latency = policy->cpuinfo.transition_latency / NSEC_PER_USEC;

	if (latency) {

		unsigned int max_delay_us = 2 * MSEC_PER_SEC;



		/*

		 * If the platform already has high transition_latency, use it

		 * as-is.

		 */

		if (latency > max_delay_us)

			return latency;



		/*

		 * For platforms that can change the frequency very fast (< 10

		 * For platforms that can change the frequency very fast (< 2

		 * us), the above formula gives a decent transition delay. But

		 * for platforms where transition_latency is in milliseconds, it

		 * ends up giving unrealistic values.
@@ -586,7 +595,7 @@ unsigned int cpufreq_policy_transition_delay_us(struct cpufreq_policy *policy) 
		 * a reasonable amount of time after which we should reevaluate

		 * the frequency.

		 */

		return min(latency * LATENCY_MULTIPLIER, (unsigned int)(2 * MSEC_PER_SEC));

		return min(latency * LATENCY_MULTIPLIER, max_delay_us);

	}



	return LATENCY_MULTIPLIER;