Commit a60a5567 authored by Sumit Gupta's avatar Sumit Gupta Committed by Viresh Kumar
Browse files

cpufreq: tegra194: use refclk delta based loop instead of udelay 



Use reference clock count based loop instead of "udelay()" for
sampling of counters to improve the accuracy of re-generated CPU
frequency. "udelay()" internally calls "WFE" which stops the
counters and results in bigger delta between the last set freq
and the re-generated value from counters. The counter sampling
window used in loop is the minimum number of reference clock
cycles which is known to give a stable value of CPU frequency.
The change also helps to reduce the sampling window from "500us"
to "<50us".

Suggested-by: default avatarAntti Miettinen <amiettinen@nvidia.com>
Signed-off-by: default avatarSumit Gupta <sumitg@nvidia.com>
Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
parent 6b121b4c

drivers/cpufreq/tegra194-cpufreq.c

+55 −17
Original line number Diff line number Diff line
@@ -5,7 +5,6 @@ 


#include <linux/cpu.h>

#include <linux/cpufreq.h>

#include <linux/delay.h>

#include <linux/dma-mapping.h>

#include <linux/module.h>

#include <linux/of.h>
@@ -21,10 +20,11 @@ 


#define KHZ                     1000

#define REF_CLK_MHZ             408 /* 408 MHz */

#define US_DELAY                500

#define CPUFREQ_TBL_STEP_HZ     (50 * KHZ * KHZ)

#define MAX_CNT                 ~0U



#define MAX_DELTA_KHZ          115200



#define NDIV_MASK              0x1FF



#define CORE_OFFSET(cpu)			(cpu * 8)
@@ -68,6 +68,7 @@ struct tegra_cpufreq_soc { 
	int maxcpus_per_cluster;

	unsigned int num_clusters;

	phys_addr_t actmon_cntr_base;

	u32 refclk_delta_min;

};



struct tegra194_cpufreq_data {
@@ -149,6 +150,8 @@ static void tegra234_read_counters(struct tegra_cpu_ctr *c) 
{

	struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();

	void __iomem *actmon_reg;

	u32 delta_refcnt;

	int cnt = 0;

	u64 val;



	actmon_reg = CORE_ACTMON_CNTR_REG(data, data->cpu_data[c->cpu].clusterid,
@@ -157,10 +160,25 @@ static void tegra234_read_counters(struct tegra_cpu_ctr *c) 
	val = readq(actmon_reg);

	c->last_refclk_cnt = upper_32_bits(val);

	c->last_coreclk_cnt = lower_32_bits(val);

	udelay(US_DELAY);



	/*

	 * The sampling window is based on the minimum number of reference

	 * clock cycles which is known to give a stable value of CPU frequency.

	 */

	do {

		val = readq(actmon_reg);

		c->refclk_cnt = upper_32_bits(val);

		c->coreclk_cnt = lower_32_bits(val);

		if (c->refclk_cnt < c->last_refclk_cnt)

			delta_refcnt = c->refclk_cnt + (MAX_CNT - c->last_refclk_cnt);

		else

			delta_refcnt = c->refclk_cnt - c->last_refclk_cnt;

		if (++cnt >= 0xFFFF) {

			pr_warn("cpufreq: problem with refclk on cpu:%d, delta_refcnt:%u, cnt:%d\n",

				c->cpu, delta_refcnt, cnt);

			break;

		}

	} while (delta_refcnt < data->soc->refclk_delta_min);

}



static struct tegra_cpufreq_ops tegra234_cpufreq_ops = {
@@ -175,6 +193,7 @@ static const struct tegra_cpufreq_soc tegra234_cpufreq_soc = { 
	.actmon_cntr_base = 0x9000,

	.maxcpus_per_cluster = 4,

	.num_clusters = 3,

	.refclk_delta_min = 16000,

};



static const struct tegra_cpufreq_soc tegra239_cpufreq_soc = {
@@ -182,6 +201,7 @@ static const struct tegra_cpufreq_soc tegra239_cpufreq_soc = { 
	.actmon_cntr_base = 0x4000,

	.maxcpus_per_cluster = 8,

	.num_clusters = 1,

	.refclk_delta_min = 16000,

};



static void tegra194_get_cpu_cluster_id(u32 cpu, u32 *cpuid, u32 *clusterid)
@@ -222,15 +242,33 @@ static inline u32 map_ndiv_to_freq(struct mrq_cpu_ndiv_limits_response 


static void tegra194_read_counters(struct tegra_cpu_ctr *c)

{

	struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();

	u32 delta_refcnt;

	int cnt = 0;

	u64 val;



	val = read_freq_feedback();

	c->last_refclk_cnt = lower_32_bits(val);

	c->last_coreclk_cnt = upper_32_bits(val);

	udelay(US_DELAY);



	/*

	 * The sampling window is based on the minimum number of reference

	 * clock cycles which is known to give a stable value of CPU frequency.

	 */

	do {

		val = read_freq_feedback();

		c->refclk_cnt = lower_32_bits(val);

		c->coreclk_cnt = upper_32_bits(val);

		if (c->refclk_cnt < c->last_refclk_cnt)

			delta_refcnt = c->refclk_cnt + (MAX_CNT - c->last_refclk_cnt);

		else

			delta_refcnt = c->refclk_cnt - c->last_refclk_cnt;

		if (++cnt >= 0xFFFF) {

			pr_warn("cpufreq: problem with refclk on cpu:%d, delta_refcnt:%u, cnt:%d\n",

				c->cpu, delta_refcnt, cnt);

			break;

		}

	} while (delta_refcnt < data->soc->refclk_delta_min);

}



static void tegra_read_counters(struct work_struct *work)
@@ -288,9 +326,8 @@ static unsigned int tegra194_calculate_speed(u32 cpu) 
	u32 rate_mhz;



	/*

	 * udelay() is required to reconstruct cpu frequency over an

	 * observation window. Using workqueue to call udelay() with

	 * interrupts enabled.

	 * Reconstruct cpu frequency over an observation/sampling window.

	 * Using workqueue to keep interrupts enabled during the interval.

	 */

	read_counters_work.c.cpu = cpu;

	INIT_WORK_ONSTACK(&read_counters_work.work, tegra_read_counters);
@@ -372,9 +409,9 @@ static unsigned int tegra194_get_speed(u32 cpu) 
		if (pos->driver_data != ndiv)

			continue;



		if (abs(pos->frequency - rate) > 115200) {

			pr_warn("cpufreq: cpu%d,cur:%u,set:%u,set ndiv:%llu\n",

				cpu, rate, pos->frequency, ndiv);

		if (abs(pos->frequency - rate) > MAX_DELTA_KHZ) {

			pr_warn("cpufreq: cpu%d,cur:%u,set:%u,delta:%d,set ndiv:%llu\n",

				cpu, rate, pos->frequency, abs(rate - pos->frequency), ndiv);

		} else {

			rate = pos->frequency;

		}
@@ -568,6 +605,7 @@ static const struct tegra_cpufreq_soc tegra194_cpufreq_soc = { 
	.ops = &tegra194_cpufreq_ops,

	.maxcpus_per_cluster = 2,

	.num_clusters = 4,

	.refclk_delta_min = 16000,

};



static void tegra194_cpufreq_free_resources(void)
@@ -684,7 +722,7 @@ static int tegra194_cpufreq_probe(struct platform_device *pdev) 


	soc = of_device_get_match_data(&pdev->dev);



	if (soc->ops && soc->maxcpus_per_cluster && soc->num_clusters) {

	if (soc->ops && soc->maxcpus_per_cluster && soc->num_clusters && soc->refclk_delta_min) {

		data->soc = soc;

	} else {

		dev_err(&pdev->dev, "soc data missing\n");