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

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Date:	Fri, 2 Oct 2015 11:17:15 -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 06/20] coresight: etm3x: unlocking tracer in default
 arch init

On 1 October 2015 at 22:47, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> 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.

Function "etm_os_unlock()" deals with ETMOSLAR and "CS_UNLOCK()" with
ETMLAR.  Both are called from "etm_init_arch_data()", which runs on
the target CPU.  One thing that I will do here is move
"etm_os_unlock()" to the beginning of "etm_init_arch_data()".  Other
than that I may be missing your point.

>
> Regards,
> --
> Alex
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