linux-kernel - Re: [PATCH v5 6/9] coresight: add support for CPU debug module

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Message-ID: <20170331005420.GA6149@leoy-linaro>
Date:   Fri, 31 Mar 2017 08:54:20 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Jonathan Corbet <corbet@....net>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Wei Xu <xuwei5@...ilicon.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Guodong Xu <guodong.xu@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, mike.leach@...aro.org,
        Suzuki.Poulose@....com
Subject: Re: [PATCH v5 6/9] coresight: add support for CPU debug module

On Thu, Mar 30, 2017 at 04:56:52PM +0100, Sudeep Holla wrote:

[...]

> > +static struct pm_qos_request debug_qos_req;
> > +static int idle_constraint = PM_QOS_DEFAULT_VALUE;
> > +module_param(idle_constraint, int, 0600);
> > +MODULE_PARM_DESC(idle_constraint, "Latency requirement in microseconds for CPU "
> > +		 "idle states (default is -1, which means have no limiation "
> > +		 "to CPU idle states; 0 means disabling all idle states; user "
> > +		 "can choose other platform dependent values so can disable "
> > +		 "specific idle states for the platform)");
> > +
> 
> NACK for this. Why you want the policy inside the driver. You can always
> do that from the user-space. I have mentioned it several times now.
> What can't you do these ?
> 
> 1. echo "what_ever_latency_you_need_in_uS" > /dev/cpu_dma_latency
> 2. echo 1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable
>    (for all cpus and their states) (1) is definitely simpler way to
>     disable deeper idle if latency = 0uS
> 
> You can always warn user about that when it's enabled via debugfs/sysfs

Thanks for suggestion, now it's clear for me.

> -- 
> Regards,
> Sudeep