Message-ID: <20171018014821.GE19504@leoy-ThinkPad-T440>
Date:   Wed, 18 Oct 2017 09:48:21 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Eduardo Valentin <edubezval@...il.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>, rui.zhang@...el.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        kevin.wangtao@...aro.org
Subject: Re: [PATCH 02/25] thermal/drivers/hisi: Remove the multiple sensors
 support

On Tue, Oct 17, 2017 at 02:07:08PM -0700, Eduardo Valentin wrote:
> On Tue, Oct 17, 2017 at 09:03:40PM +0200, Daniel Lezcano wrote:
> > On 17/10/2017 20:25, Eduardo Valentin wrote:
> > > Hello,
> > > 
> > > On Tue, Oct 17, 2017 at 02:28:27PM +0200, Daniel Lezcano wrote:
> > >> On 17/10/2017 05:54, Eduardo Valentin wrote:
> > >>> On Tue, Oct 10, 2017 at 08:02:27PM +0200, Daniel Lezcano wrote:
> > >>>> By essence, the tsensor does not really support multiple sensor at the same
> > >>>> time. It allows to set a sensor and use it to get the temperature, another
> > >>>> sensor could be switched but with a delay of 3-5ms. It is difficult to read
> > >>>> simultaneously several sensors without a big delay.
> > >>>>
> > >>>
> > >>> Is 3-5 ms enough to loose an event? Is this really a problem?
> > >>
> > >> There are several aspects:
> > >>
> > >>  - the multiple sensors is not needed here
> > > 
> > > Well, that is debatable, I cannot really agree or disagree with the
> > > above statement without understanding the use cases and most important,
> > > the location of each sensor. What is the location of each sensor?
> > > 
> > >>
> > >>  - the temperature controller is not designed to read several sensors at
> > >> the same time, we switch the sensor and that clears some internal
> > >> buffers and re-init the controller
> > > 
> > > Which is still very helpful in case you have multiple hotspots that you
> > > want to track and they are exposed on different workloads. Sacrificing
> > > the availability of sensors is something needs a better justification
> > > other than "current code uses only one".
> > > 
> > > 
> > >>
> > >>  - some boards can take 40°C in 1 sec, the temperature increase is
> > >> insanely fast and reading several sensors add an extra 15ms.
> > >>
> > > 
> > > 
> > > Ok... What is the difference in update rate with and without the switch
> > > of sensors? With the above worst case, you have about 4/6 mC/ms. Can
> > > your tsensor support that resolution for a single sensor? What is the
> > > maximum resolution a tsensor can support? What is the penalty added with
> > > switch?
> > > 
> > > Based on this data, and the above 3-5ms, that  means you would miss about
> > > ~ 3 - 4 mC while switching ( assuming tsensor can really achieve the
> > > above rate of change: 5ms * 4/6 mC /ms). Are you sure that is
> > > enough justification to drop three extra sensors?
> > 
> > Ok if I refer to the documentation the rate is 0.768 ms with the current
> > configuration.
> > 
> > The driver is currently bogus: register overwritten, bouncing interrupt,
> > unneeded lock, ... So the proposition was to remove the multiple sensors
> > support, clean the driver, and re-introduce it if there is a need.
> > 
> > If I remember correctly Leo, author of the driver, agreed on this. Leo ?
> > 
> > Note, I'm not strongly against multiple sensors support in the driver if
> > you think it is convenient but it is much simpler to remove the current
> > code as it is not used and put it back on top of a sane foundation
> > instead of circumventing that on the existing code.
> > 
> > 
> 
> I am also fine with the above strategy, as long as you are sure you are
> not breaking anyone (specially userspace). Also, it would be good to get
> a reviewed-by from hisilicon just to confirm (Leo?).

Sorry I missed to reply this patch. And yes, I have tested and
reviewed it at my side:

Reviewed-by: Leo Yan <leo.yan@...aro.org>

P.s. I am working for Linaro; I am continously co-working with
Hisilicon to maintain this driver due it's important for Hikey/Hikey960
two boards stability; this driver also is important for our daily
profiling for power and performance. Eduardo, so please let us know if
you still need ack from Hisilicon engineer.

> Besides, once you get his reviewed-by, and add it to the patches,
> can you please resend the series with the minor issues I
> mentioned (a few minor checkpatch issues and one compilation warn that
> is added to the driver after the series is applied).
> 
> > 
> > 
> > 
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