linux-kernel - Re: [RFC PATCH 15/20] coresight: etm-perf: implementing 'setup

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Date:	Thu, 1 Oct 2015 16:49:11 -0600
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>, a.p.zijlstra@...llo.nl,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, Jon Corbet <corbet@....net>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	Mike Leach <mike.leach@....com>, Tor Jeremiassen <tor@...com>,
	Al Grant <al.grant@....com>,
	Paweł Moll <pawel.moll@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 15/20] coresight: etm-perf: implementing 'setup_aux()' API

On 30 September 2015 at 05:50, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>
>> +static void *etm_setup_aux(int cpu, void **pages,
>> +                           int nr_pages, bool overwrite)
>> +{
>> +     struct coresight_device *csdev;
>> +
>> +     if (cpu == -1)
>> +             cpu = smp_processor_id();
>> +
>> +     csdev = per_cpu(csdev_sink, cpu);
>> +     if (!csdev)
>> +             return NULL;
>> +
>> +     return sink_ops(csdev)->setup_aux(csdev, cpu, pages,
>> +                                       nr_pages, overwrite);
>
> Is it guaranteed that this sink would always have .setup_aux()?

A setup_aux() is vital to the design, both on Intel and ARM.  I really
don't see how one could go without it.  I can return NULL if it hasn't
been provided - that way the setup will fail without triggering a core
dump.

>
> Regards,
> --
> Alex
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