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From:   Sumit Gupta <sumitg@nvidia.com>
To:     <viresh.kumar@linaro.org>, <rjw@rjwysocki.net>,
        <thierry.reding@gmail.com>, <jonathanh@nvidia.com>,
        <linux-pm@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
CC:     <ksitaraman@nvidia.com>, <bbasu@nvidia.com>, <sumitg@nvidia.com>
Subject: [Patch 1/2] cpufreq: tegra194: get consistent cpuinfo_cur_freq
Date:   Wed, 16 Sep 2020 22:41:16 +0530
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Frequency returned by 'cpuinfo_cur_freq' using counters is not fixed
and keeps changing slightly. This change returns a consistent value
from freq_table. If the reconstructed frequency has acceptable delta
from the last written value, then return the frequency corresponding
to the last written ndiv value from freq_table. Otherwise, print a
warning and return the reconstructed freq.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/cpufreq/tegra194-cpufreq.c | 66 ++++++++++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 9 deletions(-)

diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c
index e1d931c..d5b608d 100644
--- a/drivers/cpufreq/tegra194-cpufreq.c
+++ b/drivers/cpufreq/tegra194-cpufreq.c
@@ -180,9 +180,65 @@ static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay)
 	return (rate_mhz * KHZ); /* in KHz */
 }
 
+static void get_cpu_ndiv(void *ndiv)
+{
+	u64 ndiv_val;
+
+	asm volatile("mrs %0, s3_0_c15_c0_4" : "=r" (ndiv_val) : );
+
+	*(u64 *)ndiv = ndiv_val;
+}
+
+static void set_cpu_ndiv(void *data)
+{
+	struct cpufreq_frequency_table *tbl = data;
+	u64 ndiv_val = (u64)tbl->driver_data;
+
+	asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
+}
+
 static unsigned int tegra194_get_speed(u32 cpu)
 {
-	return tegra194_get_speed_common(cpu, US_DELAY);
+	struct cpufreq_frequency_table *table, *pos;
+	struct cpufreq_policy policy;
+	unsigned int rate;
+	u64 ndiv;
+	int err;
+
+	cpufreq_get_policy(&policy, cpu);
+	table = policy.freq_table;
+
+	/* reconstruct actual cpu freq using counters*/
+	rate = tegra194_get_speed_common(cpu, US_DELAY);
+
+	/* get last written ndiv value*/
+	err = smp_call_function_single(cpu, get_cpu_ndiv, &ndiv, true);
+	if (err) {
+		pr_err("cpufreq: Failed to get ndiv for CPU%d, ret:%d\n",
+		       cpu, err);
+		return rate;
+	}
+
+	/* if the reconstructed frequency has acceptable delta from
+	 * the last written value, then return freq corresponding
+	 * to the last written ndiv value from freq_table. This is
+	 * done to return consistent value.
+	 */
+	cpufreq_for_each_valid_entry(pos, table) {
+		if (pos->driver_data != ndiv)
+			continue;
+
+		if (abs(pos->frequency - rate) > 115200) {
+			pr_warn("cpufreq: high delta (%d) on CPU%d\n",
+				abs(pos->frequency - rate), cpu);
+			pr_warn("cpufreq: cur:%u, set:%u, set ndiv:%llu\n",
+				rate, pos->frequency, ndiv);
+		} else {
+			rate = pos->frequency;
+		}
+		break;
+	}
+	return rate;
 }
 
 static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
@@ -209,14 +265,6 @@ static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
 	return 0;
 }
 
-static void set_cpu_ndiv(void *data)
-{
-	struct cpufreq_frequency_table *tbl = data;
-	u64 ndiv_val = (u64)tbl->driver_data;
-
-	asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
-}
-
 static int tegra194_cpufreq_set_target(struct cpufreq_policy *policy,
 				       unsigned int index)
 {
-- 
2.7.4