linux-kernel - Re: Re: [PATCH v2] PM / devfreq: Use freq_table for available

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Message-id: <30733097.432311399543337408.JavaMail.weblogic@epv6ml09>
Date:	Thu, 08 May 2014 10:02:18 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	박경민 <kyungmin.park@...sung.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Re: [PATCH v2] PM / devfreq: Use freq_table for
 available_frequencies

> On 04/29/2014 01:00 PM, Saravana Kannan wrote:
> > On 04/27/2014 06:41 PM, MyungJoo Ham wrote:
> >> You are hereby changing the semmantics of the original
> >> available_frequencies node.
> >>
> >> When a frequency/voltage pair has been disabled (opp_disable), probably
> >> by opp_disable(), the frequency is no more "available".
> >> However, when the driver author supplied freq_table as well as OPP
> >> in order to see the statistics, the node will behave differently.
> >>
> >> Please do not affect the current users as long as it does not give
> >> additional benefit or fix a bug.
> > 
> > I was actually trying to stick with the semantics as it was documented.
> > The documentation for this file says it'll show frequencies that are not
> > allowed by the current min/max settings either. To me, an OPP disable
> > seems similar to some frequencies "disabled" by min/max settings.
> > 
> > Giving preference to OPP is not a hard change to do, but it seems to go
> > againsts the documented semantics.
> > 
> > Thoughts?
> 
> I'll send out another patch like you wanted -- with OPP being given
> preference over freq_table when listing frequencies.
> 
> But I would still like to hear your thoughts. As of today, there's no
> clean way to get the complete list of available frequencies that would
> give a consistent output irrespective of the temporary limits/conditions
> imposed by thermal, current limiting, etc. The round about way is to cat
> trans_stat and parse the frequencies from that.
> 
> That's why I was trying to give preference to freq_table.
> 
> Thanks,
> Saravana

The node, available_frequencies, was suggested before freq_table concept.
At that time, available_frequencies was supposed to show the list of
available OPP lists for those who use OPP for devfreq device, excluding
those disabled by OPP. (OPP lists are external to devfreq and devfreq's
min/max are internal to devfreq)

Locally, this node has been used to debug the behavior of a devfreq device.
With min/max nodes, we know the range while we cannot (easily at shell)
see which OPP points are available at the moment, where we have been able
to use available_frequencies.

We do not want to lose such capavility as long as we do not have OPP sysfs
automatically assigned to any OPP lists. If I remember correctly, we don't
have it, yet.


A. I want to minimize semantics changes in sysfs. Adding another without
interfering with previous usage is ok.
B. (more importantly) I don't want to lose the debugging capabilities.


Cheers,
MyungJoo.

> 
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
> 
> 
> 
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