linux-kernel - Re: [v3 3/5] coresight: add support for debug module

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Date:   Mon, 13 Mar 2017 16:12:14 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     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>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Guodong Xu <guodong.xu@...aro.org>,
        Haojian Zhuang <haojian.zhuang@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        mike.leach@...aro.org, Sudeep Holla <Sudeep.Holla@....com>
Subject: Re: [v3 3/5] coresight: add support for debug module

Hi Suzuki,

On Fri, Mar 10, 2017 at 02:29:53PM +0000, Suzuki K Poulose wrote:

[...]

> >>So we cannot really rely on the values in EDVIDSR which we use to make further decisions. So I
> >>am wondering if this is really guranteed to be useful.
> >
> >So this is caused by Software lock is locked?
> >
> >Section H8.4.1:
> >
> >"Reads and writes have no side-effects. A side-effect is where a
> >direct read or a direct write of a register creates
> >an indirect write of the same or another register. When the Software
> >Lock is locked, the indirect write does
> >not occur."
> 
> Yes, thats correct, further :
> 
> Section H9.2.32: EDPCSR
> 
> "For a read of EDPCSRlo from the memory-mapped interface, if EDLSR.SLK == 1, meaning
> the Software Lock is locked, then the access has no side-effects. That is, EDCIDSR,
> EDVIDSR, and EDPCSRhi are unchanged."
> 
> And since we do a CS_UNLOCK, that should be fine. Please ignore my comment.

Thanks a lot for confirmation.

[...]

> >>>+
> >>>+	put_online_cpus();
> >>>+
> >>>+	if (!debug_count++)
> >>>+		atomic_notifier_chain_register(&panic_notifier_list,
> >>>+					       &debug_notifier);
> >>>+
> >>
> >>>+	sprintf(buf, (char *)id->data, drvdata->cpu);
> >>>+	dev_info(dev, "%s initialized\n", buf);
> >>
> >>This could simply be :
> >>	dev_info(dev, "Coresight debug-CPU%d initialized\n", drvdata->cpu);
> >>
> >>and get rid of the static string and the buffer, see below.
> 
> Also we need pm_runtime_put() here to balance the pm_runtime_get_ from AMBA
> device probe. More on that below.

[...]

> Btw, I don't see any PM calls to make sure the power domain (at least the debug domain)
> is up, which could cause problems with accesses to some of these registers (leave alone the
> ones in CPU power domain), especially the EDPRSR. We could also do pm_runtime_get on the
> CPU's power domain, if the CPU is online, before we access the pcsr.

I will add pm_runtime_get/pm_runtime_put for apb clock.

But for CPU power domain, AFAIK this part is managed by PSCI but is not
controlled by pm_runtime_{put|get} pairs. So at beginning, we suggest
to use "nohlt" to ensure CPU power domain is enabled.

Please let me know if I miss some thing for this?

Thanks,
Leo Yan