Re: [PATCH v9 6/8] PM / devfreq: Introduce get_freq_range helper

From: Matthias Kaehlcke <mka@chromium.org>
To: Leonard Crestez <leonard.crestez@nxp.com>,
	Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Artur Świgoń" <a.swigon@partner.samsung.com>,
	"Abel Vesa" <abel.vesa@nxp.com>,
	"Saravana Kannan" <saravanak@google.com>,
	linux-pm@vger.kernel.org,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Lukasz Luba" <l.luba@partner.samsung.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"MyungJoo Ham" <myungjoo.ham@samsung.com>,
	"Alexandre Bailon" <abailon@baylibre.com>,
	"Georgi Djakov" <georgi.djakov@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	"Jacky Bai" <ping.bai@nxp.com>
Subject: Re: [PATCH v9 6/8] PM / devfreq: Introduce get_freq_range helper
Date: Thu, 3 Oct 2019 11:19:38 -0700	[thread overview]
Message-ID: <20191003181938.GJ87296@google.com> (raw)
In-Reply-To: <c453bb60a74b41a5192e270f286dfc81c1088449.1570044052.git.leonard.crestez@nxp.com>

On Wed, Oct 02, 2019 at 10:25:09PM +0300, Leonard Crestez wrote:
> Moving handling of min/max freq to a single function and call it from
> update_devfreq and for printing min/max freq values in sysfs.
> 
> This changes the behavior of out-of-range min_freq/max_freq: clamping
> is now done at evaluation time. This means that if an out-of-range
> constraint is imposed by sysfs and it later becomes valid then it will
> be enforced.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  drivers/devfreq/devfreq.c | 110 +++++++++++++++++++++-----------------
>  1 file changed, 62 insertions(+), 48 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 87eff789ce24..2d63692903ff 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
>
> ...
>
>  static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
>  			     char *buf)
>  {
>  	struct devfreq *df = to_devfreq(dev);
> +	unsigned long min_freq, max_freq;
>  
> -	return sprintf(buf, "%lu\n", max(df->scaling_min_freq, df->min_freq));
> +	mutex_lock(&df->lock);
> +	get_freq_range(df, &min_freq, &max_freq);

With this min/max_freq shown aren't necessarily those set through sysfs,
but the aggregated PM QoS values (plus OPP constraints).

I did some testing with a WIP patch that converts devfreq_cooling.c to
PM QoS. When reading sysfs min/max values to double check the limits
set earlier I found it utterly confusing to see the sysfs min/max values
fluctuating due to thermal throttling, and not being able to see the
configured values.

Looks like cpufreq does the same, but I'm not convinced this is a good
idea. I think we want to display the values set by userspace, as done
before managing the limits through PM QoS. Viresh, was this change of
userspace visible behavior done intentionally for cpufreq?

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