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

[Mathieu Poirier]

On 1 October 2015 at 22:47, Alexander Shishkin
<alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
> Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> writes:
>
>> On 30 September 2015 at 05:33, Alexander Shishkin
>> <alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
>>> Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>> ---
>>>>  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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