linux-kernel - Re: [RFC PATCH 03/20] coresight: etm3x: implementing 'cpu

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Date:	Thu, 1 Oct 2015 16:43:35 -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 03/20] coresight: etm3x: implementing 'cpu_id()' API

On 30 September 2015 at 05:16, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>
>> Adding an interface to lookup the CPU a tracer has been affined
>> to along with a source operation allowing external customers to
>> access it.
>>
>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>> ---
>>  drivers/hwtracing/coresight/coresight-etm3x.c | 14 ++++++++++++++
>>  include/linux/coresight.h                     |  3 +++
>>  2 files changed, 17 insertions(+)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm3x.c b/drivers/hwtracing/coresight/coresight-etm3x.c
>> index a44bc3532585..4ce9cfc06e93 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm3x.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm3x.c
>> @@ -441,6 +441,19 @@ static void etm_config_enable(void *info)
>>       spin_unlock(&drvdata->spinlock);
>>  }
>>
>> +static int etm_cpu_id(struct coresight_device *csdev)
>> +{
>> +     int cpu;
>> +     unsigned long flags;
>> +     struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> +     spin_lock_irqsave(&drvdata->spinlock, flags);
>> +     cpu = drvdata->cpu;
>> +     spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> Why do you need a spinlock here? Afaict, it never changes and if it
> would, things would go really bad really fast.

You are correct.

>
> Regards,
> --
> Alex
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