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Message-ID: <571E339E.9080306@arm.com>
Date: Mon, 25 Apr 2016 16:11:26 +0100
From: Suzuki K Poulose <Suzuki.Poulose@....com>
To: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 13/18] coresight: tmc: make sysFS and Perf mode
mutually exclusive
On 25/04/16 16:05, Mathieu Poirier wrote:
> On 25 April 2016 at 08:52, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
>> On 25/04/16 15:48, Mathieu Poirier wrote:
>>>
>>> On 25 April 2016 at 08:32, Suzuki K Poulose <Suzuki.Poulose@....com>
>>> wrote:
>>>>
>>>> On 22/04/16 18:14, Mathieu Poirier wrote:
>>
>>
>>>>> + spin_lock_irqsave(&drvdata->spinlock, flags);
>>>>> + if (drvdata->reading) {
>>>>> + ret = -EINVAL;
>>>>> + goto out;
>>>>> + }
>>>>> +
>>>>> + val = local_xchg(&drvdata->mode, mode);
>>>>> + /*
>>>>> + * In Perf mode there can be only one writer per sink. There
>>>>> + * is also no need to continue if the ETR is already operated
>>>>> + * from sysFS.
>>>>> + */
>>>>> + if (val != CS_MODE_DISABLED) {
>>>>
>>>>
>>>>
>>>> Could val be CS_MODE_PERF ? In other words, should we be checking :
>>>> if (val == CS_MODE_SYSFS) instead ?
>>>
>>>
>>> If we check for CS_MODE_SYSFS we also have to check for CS_MODE_PERF,
>>> which is two checks rather than a single one with the current
>>> solution.
>>
>>
>> I am confused now. The comment says, we want to check for sysfs mode and
>> don't continue in that case. So, we shouldn't be worried about PERF mode.
>
> You are correct about the sysFS part, but the first sentence of the
> comment also mention that in perf mode there can only be one writer
> per sink. Otherwise ring buffers for one session would end up with
> traces from other ongoing sessions, and that is not taking into
> account the buffer management nightmares it would cause.
OK, in either case, val == CS_MODE_SYSFS is much better check there, to
what we want to do
Suzuki
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