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

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Message-ID: <CAG2=9p8CMZD37KPbp+LCyDeizUHaDmw0NfqQHPvzKdCR9L0XZw@mail.gmail.com>
Date:   Wed, 11 Jan 2017 19:41:22 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        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 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.

Thanks,
Chunyan

>
> Thanks,
> Mathieu
>
>>  }
>>
>>  static phys_addr_t
>> --
>> 2.7.4
>>