Date:   Tue, 22 Feb 2022 12:03:49 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Yicong Yang <yangyicong@...ilicon.com>
CC:     <gregkh@...uxfoundation.org>, <helgaas@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <lorenzo.pieralisi@....com>,
        <will@...nel.org>, <mark.rutland@....com>,
        <mathieu.poirier@...aro.org>, <suzuki.poulose@....com>,
        <mike.leach@...aro.org>, <leo.yan@...aro.org>,
        <daniel.thompson@...aro.org>, <joro@...tes.org>,
        <john.garry@...wei.com>, <shameerali.kolothum.thodi@...wei.com>,
        <robin.murphy@....com>, <peterz@...radead.org>, <mingo@...hat.com>,
        <acme@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <coresight@...ts.linaro.org>, <linux-pci@...r.kernel.org>,
        <linux-perf-users@...r.kernel.org>,
        <iommu@...ts.linux-foundation.org>, <prime.zeng@...wei.com>,
        <liuqi115@...wei.com>, <zhangshaokun@...ilicon.com>,
        <linuxarm@...wei.com>, <song.bao.hua@...ilicon.com>
Subject: Re: [PATCH v4 3/8] hisi_ptt: Register PMU device for PTT trace

On 2022/2/21 21:26, Yicong Yang wrote:
> On 2022/2/21 19:44, Jonathan Cameron wrote:
>> On Mon, 21 Feb 2022 16:43:02 +0800
>> Yicong Yang <yangyicong@...ilicon.com> wrote:
>>
>>> Register PMU device of PTT trace, then users can use
>>> trace through perf command. The driver makes use of perf
>>> AUX trace and support following events to configure the
>>> trace:
>>>
>>> - filter: select Root port or Endpoint to trace
>>> - type: select the type of traced TLP headers
>>> - direction: select the direction of traced TLP headers
>>> - format: select the data format of the traced TLP headers
>>>
>>> This patch adds the PMU driver part of PTT trace. The perf
>>> command support of PTT trace is added in the following
>>> patch.
>>>
>>> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
>>
>> A few minor comments inline.
>>
> 
> Thanks for the comments!
> 
>> Thanks,
>>
>> Jonathan
>>
>>> +static int hisi_ptt_trace_init_filter(struct hisi_ptt *hisi_ptt, u64 config)
>>> +{
>>> +	unsigned long val, port_mask = hisi_ptt->port_mask;
>>> +	struct hisi_ptt_filter_desc *filter;
>>> +	int ret = -EINVAL;
>>> +
>>> +	hisi_ptt->trace_ctrl.is_port = FIELD_GET(HISI_PTT_PMU_FILTER_IS_PORT, config);
>>> +	val = FIELD_GET(HISI_PTT_PMU_FILTER_VAL_MASK, config);
>>> +
>>> +	/*
>>> +	 * Port filters are defined as bit mask. For port filters, check
>>> +	 * the bits in the @val are within the range of hisi_ptt->port_mask
>>> +	 * and whether it's empty or not, otherwise user has specified
>>> +	 * some unsupported root ports.
>>> +	 *
>>> +	 * For Requester ID filters, walk the available filter list to see
>>> +	 * whether we have one matched.
>>> +	 */
>>> +	if (!hisi_ptt->trace_ctrl.is_port) {
>>> +		list_for_each_entry(filter, &hisi_ptt->req_filters, list)
>>> +			if (val == hisi_ptt_get_filter_val(filter->pdev)) {
>>> +				ret = 0;
>>> +				break;
>>> +			}
>>> +	} else if (bitmap_subset(&val, &port_mask, BITS_PER_LONG)) {
>>> +		ret = 0;
>>> +	}
>>> +
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	hisi_ptt->trace_ctrl.filter = val;
>>> +	return 0;
>>> +}
>>> +
>>> +static int hisi_ptt_pmu_event_init(struct perf_event *event)
>>> +{
>>> +	struct hisi_ptt *hisi_ptt = to_hisi_ptt(event->pmu);
>>> +	struct hisi_ptt_trace_ctrl *ctrl = &hisi_ptt->trace_ctrl;
>>> +	int ret;
>>> +	u32 val;
>>> +
>>> +	if (event->attr.type != hisi_ptt->hisi_ptt_pmu.type)
>>> +		return -ENOENT;
>>> +
>>> +	mutex_lock(&hisi_ptt->mutex);
>>> +
>>> +	ret = hisi_ptt_trace_init_filter(hisi_ptt, event->attr.config);
>>> +	if (ret < 0)
>>> +		goto out;
>>> +
>>> +	val = FIELD_GET(HISI_PTT_PMU_DIRECTION_MASK, event->attr.config);
>>> +	ret = hisi_ptt_trace_valid_config_onehot(val, hisi_ptt_trace_available_direction,
>>> +						 ARRAY_SIZE(hisi_ptt_trace_available_direction));
>>> +	if (ret < 0)
>>> +		goto out;
>>> +	ctrl->direction = val;
>>> +
>>> +	val = FIELD_GET(HISI_PTT_PMU_TYPE_MASK, event->attr.config);
>>> +
>>
>> For consistency, no blank line here.
>>
> 
> will drop it.
> 
>>> +	ret = hisi_ptt_trace_valid_config(val, hisi_ptt_trace_available_type,
>>> +					  ARRAY_SIZE(hisi_ptt_trace_available_type));
>>> +	if (ret < 0)
>>> +		goto out;
>>> +	ctrl->type = val;
>>> +
>>> +	val = FIELD_GET(HISI_PTT_PMU_FORMAT_MASK, event->attr.config);
>>> +	ret = hisi_ptt_trace_valid_config_onehot(val, hisi_ptt_trace_availble_format,
>>> +						 ARRAY_SIZE(hisi_ptt_trace_availble_format));
>>> +	if (ret < 0)
>>> +		goto out;
>>> +	ctrl->format = val;
>>> +
>>> +out:
>>> +	mutex_unlock(&hisi_ptt->mutex);
>>> +	return ret;
>>> +}
>>
>> ...
>>
>>> +
>>> +static void hisi_ptt_pmu_start(struct perf_event *event, int flags)
>>> +{
>>> +	struct hisi_ptt *hisi_ptt = to_hisi_ptt(event->pmu);
>>> +	struct perf_output_handle *handle = &hisi_ptt->trace_ctrl.handle;
>>> +	struct hw_perf_event *hwc = &event->hw;
>>> +	struct hisi_ptt_pmu_buf *buf;
>>> +	int cpu = event->cpu;
>>> +	int ret;
>>> +
>>> +	hwc->state = 0;
>>> +	mutex_lock(&hisi_ptt->mutex);
>>> +	if (hisi_ptt->trace_ctrl.status == HISI_PTT_TRACE_STATUS_ON) {
>>> +		pci_dbg(hisi_ptt->pdev, "trace has already started\n");
>>> +		goto stop;
>>
>> If it is already started setting the state to STOPPED without doing anything
>> to change the hardware state doesn't feel right.
> 
> I think it won't happen as we follow the order to stop the hardware and then
> set the HISI_PTT_TRACE_STATUS_OFF flags.
> 
> But it makes me read start/stop process again and I find that I should set the
> HISI_PTT_TRACE_STATUS_ON first before I start the hardware. Now it maybe problematic.
> 
>> I'm assuming we only get here as a result of a bug, so perhaps its fine
>> to do this.
>>
>>> +	}
>>> +
>>> +	if (cpu == -1)
>>> +		cpu = hisi_ptt->trace_ctrl.default_cpu;
>>> +
>>> +	/*
>>> +	 * Handle the interrupt on the same cpu which starts the trace to avoid
>>> +	 * context mismatch. Otherwise we'll trigger the WARN from the perf
>>> +	 * core in event_function_local().
>>> +	 */
>>> +	WARN_ON(irq_set_affinity(pci_irq_vector(hisi_ptt->pdev, HISI_PTT_TRACE_DMA_IRQ),
>>> +				 cpumask_of(cpu)));
>>> +
>>> +	ret = hisi_ptt_alloc_trace_buf(hisi_ptt);
>>> +	if (ret) {
>>> +		pci_dbg(hisi_ptt->pdev, "alloc trace buf failed, ret = %d\n", ret);
>>> +		goto stop;
>>> +	}
>>> +
>>> +	buf = perf_aux_output_begin(handle, event);
>>> +	if (!buf) {
>>> +		pci_dbg(hisi_ptt->pdev, "aux output begin failed\n");
>>> +		goto stop;
>>> +	}
>>> +
>>> +	buf->pos = handle->head % buf->length;
>>> +
>>> +	ret = hisi_ptt_trace_start(hisi_ptt);
>>> +	if (ret) {
>>> +		pci_dbg(hisi_ptt->pdev, "trace start failed, ret = %d\n", ret);
>>> +		perf_aux_output_end(handle, 0);
>>> +		goto stop;
>>> +	}
>>> +
>>> +	mutex_unlock(&hisi_ptt->mutex);
>>> +	return;
>>> +stop:
>>> +	event->hw.state |= PERF_HES_STOPPED;
>>> +	mutex_unlock(&hisi_ptt->mutex);
>>> +}
>>> +
>>
>> ...
>>
>>> +static int hisi_ptt_register_pmu(struct hisi_ptt *hisi_ptt)
>>> +{
>>> +	u16 core_id, sicl_id;
>>> +	char *pmu_name;
>>> +	int ret;
>>> +	u32 reg;
>>> +
>>> +	hisi_ptt->hisi_ptt_pmu = (struct pmu) {
>>> +		.module		= THIS_MODULE,
>>> +		.capabilities	= PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE,
>>> +		.task_ctx_nr	= perf_sw_context,
>>> +		.attr_groups	= hisi_ptt_pmu_groups,
>>> +		.event_init	= hisi_ptt_pmu_event_init,
>>> +		.setup_aux	= hisi_ptt_pmu_setup_aux,
>>> +		.free_aux	= hisi_ptt_pmu_free_aux,
>>> +		.start		= hisi_ptt_pmu_start,
>>> +		.stop		= hisi_ptt_pmu_stop,
>>> +		.add		= hisi_ptt_pmu_add,
>>> +		.del		= hisi_ptt_pmu_del,
>>> +	};
>>> +
>>> +	reg = readl(hisi_ptt->iobase + HISI_PTT_LOCATION);
>>> +	core_id = FIELD_GET(HISI_PTT_CORE_ID, reg);
>>> +	sicl_id = FIELD_GET(HISI_PTT_SICL_ID, reg);
>>> +
>>> +	pmu_name = devm_kasprintf(&hisi_ptt->pdev->dev, GFP_KERNEL, "hisi_ptt%u_%u",
>>> +				  sicl_id, core_id);
>>> +	if (!pmu_name)
>>> +		return -ENOMEM;
>>> +
>>> +	ret = perf_pmu_register(&hisi_ptt->hisi_ptt_pmu, pmu_name, -1);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	return devm_add_action_or_reset(&hisi_ptt->pdev->dev,
>>> +					hisi_ptt_unregister_pmu,
>>> +					&hisi_ptt->hisi_ptt_pmu);
>>
>> This result in the cleanup of the driver being slightly out of order wrt to
>> the setup as we have the filters cleared after this (in remove())
>> Ideally the remove() ordering should be the precise reverse of the
>> probe() order except where it is necessary to deviate from that and
>> in those deviations I'd expect to see a comment saying why.
>>

Yes, it's a bit out of order here and I'll reorder it.

But it's also ok to clear the filters before unregister the pmu as the pmu
does not highly depend on the filters. If the filters list is empty we'll fail
in pmu->event_init(). So I think there won't be a problem if we clear
the filters prior to unregister the pmu on removal.

>> So either clear up the filters using a devm_add_action_or_reset()
>> or do a manual unregister of the pmu in remove. I prefer the
>> devm_add_action_or_reset for hisi_ptt_release_filters() option.
>>

Sure. But it maybe better to manually unregister the pmu device once
into the remove() as we also release the DMA buffers in remove() which
are used by the pmu. The order in the probe()/removal() will be like:

void hisi_ptt_remove(struct pci_dev *pdev)
{
	struct hisi_ptt *hisi_ptt = pci_get_drvdata(pdev);

	bus_unregister_notifier(&pci_bus_type, &hisi_ptt->hisi_ptt_nb);

	/* Cancel any work that has been queued */
	cancel_delayed_work_sync(&hisi_ptt->work);

	perf_pmu_unregister(&hisi_ptt->hisi_ptt_pmu);

	hisi_ptt_free_trace_buf(hisi_ptt);
	hisi_ptt_release_filters(hisi_ptt);
}

I also found the check of trace status in remove() is a bit redundant
and I'd like to drop the check as there's won't be any active perf
session and the trace can only be started/stopped by pmu.

>> There may well not be a race here, but it is always good to avoid
>> reviewers having to think about whether there might be one!
>>

Thanks for the suggestion. Will follow this good manner to avoid
potential problems.

Regards,
Yicong

>> Note that other reviewers may have different views on this however
>> so perhaps go with what they say as this subsystem isn't my area
>> of expertise!
>>
> 
> I'd like to think a bit more time about the orders here before reply. :)
> 
> Thanks,
> Yicong
> 
>>> +}
>>> +
>>>  /*
>>>   * The DMA of PTT trace can only use direct mapping, due to some
>>>   * hardware restriction. Check whether there is an IOMMU or the
>>> @@ -337,6 +826,12 @@ static int hisi_ptt_probe(struct pci_dev *pdev,
>>>  
>>>  	hisi_ptt_init_ctrls(hisi_ptt);
>>>  
>>> +	ret = hisi_ptt_register_pmu(hisi_ptt);
>>> +	if (ret) {
>>> +		pci_err(pdev, "failed to register pmu device, ret = %d", ret);
>>> +		return ret;
>>> +	}
>>> +
>>>  	return 0;
>>>  }
>>>  
>> .
>>
> .
> 

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