Re: [PATCH v4 3/8] hisi_ptt: Register PMU device for PTT trace

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Yicong Yang <yangyicong@hisilicon.com>
Cc: <gregkh@linuxfoundation.org>, <helgaas@kernel.org>,
	<alexander.shishkin@linux.intel.com>, <lorenzo.pieralisi@arm.com>,
	<will@kernel.org>, <mark.rutland@arm.com>,
	<mathieu.poirier@linaro.org>, <suzuki.poulose@arm.com>,
	<mike.leach@linaro.org>, <leo.yan@linaro.org>,
	<daniel.thompson@linaro.org>, <joro@8bytes.org>,
	<john.garry@huawei.com>, <shameerali.kolothum.thodi@huawei.com>,
	<robin.murphy@arm.com>, <peterz@infradead.org>,
	<mingo@redhat.com>, <acme@kernel.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<coresight@lists.linaro.org>, <linux-pci@vger.kernel.org>,
	<linux-perf-users@vger.kernel.org>,
	<iommu@lists.linux-foundation.org>, <prime.zeng@huawei.com>,
	<liuqi115@huawei.com>, <zhangshaokun@hisilicon.com>,
	<linuxarm@huawei.com>, <song.bao.hua@hisilicon.com>
Subject: Re: [PATCH v4 3/8] hisi_ptt: Register PMU device for PTT trace
Date: Mon, 21 Feb 2022 11:44:28 +0000	[thread overview]
Message-ID: <20220221114428.000062cd@Huawei.com> (raw)
In-Reply-To: <20220221084307.33712-4-yangyicong@hisilicon.com>

On Mon, 21 Feb 2022 16:43:02 +0800
Yicong Yang <yangyicong@hisilicon.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@hisilicon.com>

A few minor comments inline.

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.

> +	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'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.

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.

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!

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!

> +}
> +
>  /*
>   * 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;
>  }
>  