linux-kernel - Re: [RFC PATCH 06/20] coresight: etm3x: unlocking tracer in default arch init

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Message-ID: <87vbap3mgz.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Fri, 02 Oct 2015 07:47:56 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
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\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-doc@...r.kernel.org,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 06/20] coresight: etm3x: unlocking tracer in default arch init

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> On 30 September 2015 at 05:33, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>>
>>> Calling function 'smp_call_function_single()' to unlock the
>>> tracer and calling it right after to perform the default
>>> initialisation doesn't make sense.
>>>
>>> Moving 'etm_os_unlock()' just before making the default
>>> initialisation results in the same outcome while saving
>>> one call to 'smp_call_function_single()'.
>>>
>>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>>> ---
>>>  drivers/hwtracing/coresight/coresight-etm3x.c | 8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-etm3x.c b/drivers/hwtracing/coresight/coresight-etm3x.c
>>> index c6880c1ade55..a4c158df0fef 100644
>>> --- a/drivers/hwtracing/coresight/coresight-etm3x.c
>>> +++ b/drivers/hwtracing/coresight/coresight-etm3x.c
>>> @@ -1867,6 +1867,11 @@ static void etm_init_arch_data(void *info)
>>>        * certain registers might be ignored.
>>>        */
>>>       etm_clr_pwrdwn(drvdata);
>>> +
>>> +     /* Make sure all registers are accessible */
>>> +     etm_os_unlock(drvdata);
>>
>> In case of co-processor register access, this will end up unlocking the
>> local ETM instead of the one on target cpu, by the looks of it.
>
> "etm_init_arch_data()" is also called from "smp_function_calls()" and
> as such, will end up executing the correct CPU.

Yes, but it doesn't unlock the OSLAR register, which also needs to be
done on target cpu.

Regards,
--
Alex
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