clk: qcom: clk-cpu-osm: Advertise transition latency to cpufreq

The cpufreq subsystem can be made aware of the frequency transition
latency for governors to make better default value choices, such as rate
limits and sampling rates.

This also exposes the transition latency to userspace through the
cpuinfo_transition_latency sysfs node.

Signed-off-by: Danny Lin <danny@kdrag0n.dev>

Author: kdrag0n

drivers/clk/qcom/clk-cpu-osm.c

@@ -43,6 +43,7 @@
 
 #define OSM_INIT_RATE			300000000UL
 #define XO_RATE				19200000UL
+#define RATE_LIMIT_US			10000
 #define OSM_TABLE_SIZE			40
 #define SINGLE_CORE			1
 #define MAX_CLUSTER_CNT			3
@@ -675,8 +676,9 @@ osm_set_index(struct clk_osm *c, unsigned int index)
 
 	/* The old rate needs time to settle before it can be changed again */
 	delta_us = ktime_us_delta(ktime_get_boottime(), parent->last_update);
-	if (delta_us < 10000)
-		usleep_range(10000 - delta_us, 11000 - delta_us);
+	if (delta_us < RATE_LIMIT_US)
+		usleep_range(RATE_LIMIT_US - delta_us,
+			     (RATE_LIMIT_US + 1000) - delta_us);
 	parent->last_update = ktime_get_boottime();
 
 	clk_set_rate(c->hw.clk, clk_round_rate(c->hw.clk, rate));
@@ -790,6 +792,7 @@ static int osm_cpufreq_cpu_init(struct cpufreq_policy *policy)
 		goto err;
 	}
 
+	policy->cpuinfo.transition_latency = RATE_LIMIT_US;
 	policy->driver_data = c;
 	return 0;