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

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Message-ID: <e2710e1c-471d-2645-5ce0-30e222c85b52@arm.com>
Date:   Wed, 11 Jan 2017 13:59:38 +0000
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     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 11/01/17 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.


Suzuki