linux-kernel - [PATCH v5 16/36] PM / devfreq: tegra20: Adjust clocks conversion ratio and polling interval

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Date:   Fri, 14 Aug 2020 03:06:01 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Mikko Perttunen <cyndis@...si.fi>
Cc:     linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org
Subject: [PATCH v5 16/36] PM / devfreq: tegra20: Adjust clocks conversion ratio and polling interval

The current conversion ratio results in a higher frequency than needed,
that is not very actual now since the Display Controller driver got
support for memory bandwidth management and hence memory frequency can
go lower now without bad consequences. Since memory freq now goes to a
lower rates, the responsiveness of interactive applications become worse
due to a quite high polling interval value that is currently set to 500ms.
Changing polling interval to 30ms results in a good responsiveness of the
system.

Acked-by: Chanwoo Choi <cw00.choi@...sung.com>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 drivers/devfreq/tegra20-devfreq.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/devfreq/tegra20-devfreq.c b/drivers/devfreq/tegra20-devfreq.c
index bc43284996de..ebfc5ac9e5c3 100644
--- a/drivers/devfreq/tegra20-devfreq.c
+++ b/drivers/devfreq/tegra20-devfreq.c
@@ -79,16 +79,12 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
 
 	/*
 	 * EMC_COUNT returns number of memory events, that number is lower
-	 * than the number of clocks. Conversion ratio of 1/8 results in a
-	 * bit higher bandwidth than actually needed, it is good enough for
-	 * the time being because drivers don't support requesting minimum
-	 * needed memory bandwidth yet.
-	 *
-	 * TODO: adjust the ratio value once relevant drivers will support
-	 * memory bandwidth management.
+	 * than the number of total EMC clocks over the sampling period.
+	 * The clocks number is converted to maximum possible number of
+	 * memory events using the ratio of 1/4.
 	 */
 	stat->busy_time = readl_relaxed(tegra->regs + MC_STAT_EMC_COUNT);
-	stat->total_time = readl_relaxed(tegra->regs + MC_STAT_EMC_CLOCKS) / 8;
+	stat->total_time = readl_relaxed(tegra->regs + MC_STAT_EMC_CLOCKS) / 4;
 	stat->current_frequency = clk_get_rate(tegra->emc_clock);
 
 	writel_relaxed(EMC_GATHER_CLEAR, tegra->regs + MC_STAT_CONTROL);
@@ -98,7 +94,7 @@ static int tegra_devfreq_get_dev_status(struct device *dev,
 }
 
 static struct devfreq_dev_profile tegra_devfreq_profile = {
-	.polling_ms	= 500,
+	.polling_ms	= 30,
 	.target		= tegra_devfreq_target,
 	.get_dev_status	= tegra_devfreq_get_dev_status,
 };
-- 
2.27.0