linux-kernel - Re: [PATCH V6 21/26] coresight: etm-perf: new PMU driver for ETM tracers

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Date:	Fri, 11 Dec 2015 14:18:09 -0700
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	Mike Leach <mike.leach@....com>,
	"Jeremiassen, Tor" <tor@...com>, Al Grant <al.grant@....com>,
	fainelli@...adcom.com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V6 21/26] coresight: etm-perf: new PMU driver for ETM tracers

On 11 December 2015 at 08:18, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>
>> +static void etm_event_start(struct perf_event *event, int flags)
>> +{
>> +     int cpu = smp_processor_id();
>> +     struct etm_cpu_data *cpu_data;
>> +     struct etm_event_data *event_data;
>> +     struct perf_output_handle *handle = this_cpu_ptr(&ctx_handle);
>> +     struct coresight_device *sink, *csdev = per_cpu(csdev_src, cpu);
>> +
>> +     if (!csdev)
>> +             goto fail;
>> +
>> +     /*
>> +      * Deal with the ring buffer API and get a handle on the
>> +      * session's information.
>> +      */
>> +     event_data = perf_aux_output_begin(handle, event);
>> +     if (WARN_ON_ONCE(!event_data))
>> +             goto fail;
>
> Hmm, perf_aux_output_begin() returning NULL is not WARN-worthy and is
> actually a normal situation, for example, if the buffer is not
> configured yet (which like I suggested in the other email should be a
> separate thing from the *event* configuration).
>
> perf_aux_output_begin() will also return NULL if there's no room in the
> buffer.

You are correct - I'll revise this.

>
> Regards,
> --
> Alex
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