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Subject[PATCH] cpufreq: Honour transition_latency over transition_delay_us
Date
Some platforms like Arm's Juno can have a high transition latency that
can be larger than the 2ms cap introduced. If a driver report
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: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Qais Yousef <qyousef@layalina.io>
---
drivers/cpufreq/cpufreq.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 66cef33c4ec7..926a51cb7e52 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -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;
--
2.34.1

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