Date: Thu, 3 Mar 2016 08:29:44 -0800
From: Eduardo Valentin <edubezval@gmail.com>
To: Leo Yan <leo.yan@linaro.org>
Cc: Wei Xu <xuwei5@hisilicon.com>, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, Zhang Rui <rui.zhang@intel.com>,
        kongxinwei <kong.kongxinwei@hisilicon.com>,
        Javi Merino <javi.merino@arm.com>,
        Punit Agrawal <Punit.Agrawal@arm.com>,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 1/5] thermal: change "hysteresis" as optional property
Message-ID: <20160303162942.GA2445@localhost.localdomain>
References: <1456458227-12950-1-git-send-email-leo.yan@linaro.org>
 <1456458227-12950-2-git-send-email-leo.yan@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1456458227-12950-2-git-send-email-leo.yan@linaro.org>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 975
Lines: 23

Hi Leo,

On Fri, Feb 26, 2016 at 11:43:43AM +0800, Leo Yan wrote:
> The property "hysteresis" is mandatory for trip points, so if without
> it the thermal zone cannot register successfully. But "hysteresis" is
> ignored in the thermal subsystem and only inquired by several thermal
> sensor drivers.

I am not sure this a good direction to go. Remember that Linux
implementation not necessarily has to be the implication of the DT
binding. Hysteresis is a property that plays a significant role on
thermal control systems, which in many cases avoid overshooting cooling
actions. Having the DT writer to explicitly set it to 0 means that zone
does not suffer of overshooting and does not need hysteresis.

If the Linux thermal subsystem has a problem with handling hysteresis, I
would rather fix Linux code than relaxing the DT binding. Or if you
still believe hysteresis is really optional, I would prefer to see a
better justification than "Linux ignores it".

BR,

Eduardo