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

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Date:   Thu, 30 Mar 2017 09:03:43 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        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>,
        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,
        "Suzuki K. Poulose" <Suzuki.Poulose@....com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v5 6/9] coresight: add support for CPU debug module

On Wed, Mar 29, 2017 at 03:56:23PM +0100, Mike Leach wrote:

[...]

> >> > +   /*
> >> > +    * Unfortunately the CPU cannot be powered up, so return
> >> > +    * back and later has no permission to access other
> >> > +    * registers. For this case, should set 'idle_constraint'
> >> > +    * to ensure CPU power domain is enabled!
> >> > +    */
> >> > +   if (!(drvdata->edprsr & EDPRSR_PU)) {
> >> > +           pr_err("%s: power up request for CPU%d failed\n",
> >> > +                   __func__, drvdata->cpu);
> >> > +           goto out;
> >> > +   }
> >> > +
> >> > +out_powered_up:
> >> > +   debug_os_unlock(drvdata);
> >> > +
> >> > +   /*
> >> > +    * At this point the CPU is powered up, so set the no powerdown
> >> > +    * request bit so we don't lose power and emulate power down.
> >> > +    */
> >> > +   drvdata->edprsr = readl(drvdata->base + EDPRCR);
> >> > +   drvdata->edprsr |= EDPRCR_COREPURQ | EDPRCR_CORENPDRQ;
> >>
> >> If we are here the core is already up.  Shouldn't we need to set
> >> EDPRCR_CORENPDRQ only?
> >
> > Yeah. Will fix.
> 
> No - EDPRCR_COREPURQ and EDPRCR_CORENPDRQ have different semantics and purposes
> 
> EDPRCR_COREPURQ is in the debug power domain an is tied to an external
> debug request that should be an input to the external (to the PE)
> system power controller.
> The requirement is that the system power controller powers up the core
> domain and does not power it down while it remains asserted.
> 
> EDPRCR_CORENPDRQ is in the core power domain and thus to the specific
> core only. This ensures that any power control software running on
> that core should emulate a power down if this is set to one.

I'm curious the exact meaning for "power control software".

Does it mean EDPRCR_CORENPDRQ should be checked by kernel or PSCI
liked code in ARM trusted firmware to avoid to run CPU power off flow?

Or will EDPRCR_CORENPDRQ assert CPU external signal to notify power
controller so power controller emulate a power down?

> We cannot know the power control design of the system, so the safe
> solution is to set both bits.

Thanks a lot for the suggestion. Will set both bits.

Thanks,
Leo Yan