linux-kernel - Re: [PATCH] coresight: STM: Balance enable/disable

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Message-ID: <CAG2=9p9ZW1tsKb83yRiQwOuj75VWdcB+i=cCUvevyLyH74Qz2g@mail.gmail.com>
Date:   Fri, 13 Jan 2017 10:10:34 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, gregkh@...uxfoundation.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] coresight: STM: Balance enable/disable

On 11 January 2017 at 21:59, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
> On 11/01/17 11:41, Chunyan Zhang wrote:
>>
>> On 11 January 2017 at 01:36, Mathieu Poirier <mathieu.poirier@...aro.org>
>> wrote:
>>>
>>> On Tue, Jan 10, 2017 at 11:21:55AM +0000, Suzuki K Poulose wrote:
>>>>
>>>> The stm is automatically enabled when an application sets the policy
>>>> via ->link() call back by using coresight_enable(), which keeps the
>>>> refcount of the current users of the STM. However, the unlink() callback
>>>> issues stm_disable() directly, which leaves the STM turned off, without
>>>> the coresight layer knowing about it. This prevents any further uses
>>>> of the STM hardware as the coresight layer still thinks the STM is
>>>> turned on and doesn't issue an stm_enable(). Even manually enabling
>>>> the STM via sysfs can't really enable the hw.
>>>>
>>>> e.g,
>>>>
>>>> $ echo 1 > $CS_DEVS/$ETR/enable_sink
>>>> $ mkdir -p $CONFIG_FS/stp-policy/$source.0/stm_test/
>>>> $ echo 32768 65535 > $CONFIG_FS/stp-policy/$source.0/stm_test/channels
>>>> $ echo 64 > $CS_DEVS/$source/traceid
>>>> $ ./stm_app
>>>> Sending 64000 byte blocks of pattern 0 at 0us intervals
>>>> Success to map channel(32768~32783) to 0xffffa95fa000
>>>> Sending on channel 32768
>>>> $ dd if=/dev/$ETR of=~/trace.bin.1
>>>> 597+1 records in
>>>> 597+1 records out
>>>> 305920 bytes (306 kB) copied, 0.399952 s, 765 kB/s
>>>> $ ./stm_app
>>>> Sending 64000 byte blocks of pattern 0 at 0us intervals
>>>> Success to map channel(32768~32783) to 0xffff7e9e2000
>>>> Sending on channel 32768
>>>> $ dd if=/dev/$ETR of=~/trace.bin.2
>>>> 0+0 records in
>>>> 0+0 records out
>>>> 0 bytes (0 B) copied, 0.0232083 s, 0.0 kB/s
>>>>
>>>> Note that we don't get any data from the ETR for the second session.
>>>>
>>>> Also dmesg shows :
>>>>
>>>> [   77.520458] coresight-tmc 20800000.etr: TMC-ETR enabled
>>>> [   77.537097] coresight-replicator etr_replicator@...90000: REPLICATOR
>>>> enabled
>>>> [   77.558828] coresight-replicator main_replicator@...a0000: REPLICATOR
>>>> enabled
>>>> [   77.581068] coresight-funnel 208c0000.main_funnel: FUNNEL inport 0
>>>> enabled
>>>> [   77.602217] coresight-tmc 20840000.etf: TMC-ETF enabled
>>>> [   77.618422] coresight-stm 20860000.stm: STM tracing enabled
>>>> [  139.554252] coresight-stm 20860000.stm: STM tracing disabled
>>>>  # End of first tracing session
>>>> [  146.351135] coresight-tmc 20800000.etr: TMC read start
>>>> [  146.514486] coresight-tmc 20800000.etr: TMC read end
>>>>  # Note that the STM is not turned on via
>>>> stm_generic_link()->coresight_enable()
>>>>  # and hence none of the components are turned on.
>>>> [  152.479080] coresight-tmc 20800000.etr: TMC read start
>>>> [  152.542632] coresight-tmc 20800000.etr: TMC read end
>>>>
>>>> This patch balances the unlink operation by using the
>>>> coresight_disable(),
>>>> keeping the coresight layer in sync with the hardware state.
>>>>
>>>> Fixes: commit 237483aa5cf43 ("coresight: stm: adding driver for
>>>> CoreSight STM component")
>>>> Cc: Pratik Patel <pratikp@...eaurora.org>
>>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>>> Cc: Chunyan Zhang <zhang.chunyan@...aro.org>
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> Cc: stable@...r.kernel.org # 4.7+
>>>> Reported-by: Robert Walker <robert.walker@....com>
>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>>>> ---
>>>>  drivers/hwtracing/coresight/coresight-stm.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/hwtracing/coresight/coresight-stm.c
>>>> b/drivers/hwtracing/coresight/coresight-stm.c
>>>> index 3524452..57b7330 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-stm.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-stm.c
>>>> @@ -356,7 +356,7 @@ static void stm_generic_unlink(struct stm_data
>>>> *stm_data,
>>>>       if (!drvdata || !drvdata->csdev)
>>>>               return;
>>>>
>>>> -     stm_disable(drvdata->csdev, NULL);
>>>> +     coresight_disable(drvdata->csdev);
>>>
>>>
>>> This looks valid to me.
>>>
>>> Chunyan, any reason to use stm_disable() directly rather than calling it
>>> as part
>>> of the device OPS in coresight_disable()?
>>
>>
>> I don't think there's some special reason for this. I simply hadn't
>> noticed that these two operations didn't use two balanced functions.
>
>
> Please can I have an Ack/Reviewed -by on it, so that we can push it
> as a fix.

Sure, I've had a run with this patch, it works well, so,
Reviewed-by: Chunyan Zhang <zhang.chunyan@...aro.org>

Thanks,
Chunyan

>
>
> Suzuki
>