linux-kernel - Re: [PATCH v3 02/13] coresight: etb10: Fix handling of perf mode

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Date:   Tue, 31 Jul 2018 22:32:39 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mike.leach@...aro.org, robert.walker@....com,
        coresight@...ts.linaro.org
Subject: Re: [PATCH v3 02/13] coresight: etb10: Fix handling of perf mode

On 07/31/2018 06:07 PM, Mathieu Poirier wrote:
> Hello,
> 
> On Thu, Jul 26, 2018 at 01:54:40PM +0100, Suzuki K Poulose wrote:
>> If the ETB is already enabled in sysfs mode, the ETB reports
>> success even if a perf mode is requested. Fix this by checking
>> the requested mode.
>>
>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   drivers/hwtracing/coresight/coresight-etb10.c | 8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
>> index 306119e..e5808fd 100644
>> --- a/drivers/hwtracing/coresight/coresight-etb10.c
>> +++ b/drivers/hwtracing/coresight/coresight-etb10.c
>> @@ -148,8 +148,12 @@ static int etb_enable(struct coresight_device *csdev, u32 mode)
>>   		return -EBUSY;
>>   
>>   	/* Nothing to do, the tracer is already enabled. */
>> -	if (val == CS_MODE_SYSFS)
>> -		goto out;
>> +	if (val == CS_MODE_SYSFS) {
>> +		if (mode == CS_MODE_SYSFS)
>> +			goto out;
>> +		else
>> +			return -EBUSY;
>> +	}
> 
> How about:
> 
>          if (val == CS_MODE_PERF)
>                  return -EBUSY;
>   
> +       /* Don't let perf disturb sysFS sessions */
> +       if (val == CS_MODE_SYSFS && mode = CS_MODE_PERF)
> +               return -EBUSY;
> +
>          /* Nothing to do, the tracer is already enabled. */
>          if (val == CS_MODE_SYSFS)
>                  goto out;
> 
> 
> I just find it more readable that way.

Sure, thats fine by me.

Cheers
Suzuki