Re: [PATCH v5 3/8] hisi_ptt: Register PMU device for PTT trace

[Yicong Yang]

On 2022/3/8 20:06, Jonathan Cameron wrote:
> On Tue, 8 Mar 2022 19:13:08 +0800
> Yicong Yang <yangyicong@xxxxxxxxxx> wrote:
> 
>> On 2022/3/8 18:21, Jonathan Cameron wrote:
>>> On Tue, 8 Mar 2022 16:49:25 +0800
>>> Yicong Yang <yangyicong@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>  
>>>
>>> It seems to me that you ended up doing both suggestions for
>>> how to clean up the remove order when it was meant to be
>>> a question of picking one or the other.
>>>
>>> Otherwise this looks good to me - so with that tidied up
>>>   
>>
>> Hi Jonathan,
>>
>> Thanks for the comments. I'd like to illustrate the reason why I decide to
>> manually unregister the PMU device.
>>
>> The DMA buffers are devm allocated when necessary. They're only allocated
>> when user is going to use the PTT in the first time after the driver's probe,
>> so when driver removal the buffers are released prior to the PMU device's
>> unregistration. I think there's a race condition.
>>
>> IIUC, The PMU device(as the user interface) should be unregistered first then
>> we're safe to free the DMA buffers. But unregister the PMU device by devm
>> cannot keep that order.
> 
> Ok. Please add a comment in the remove() giving this reasoning.
> 

Sure will add a comment for the reason why we need this manual unregistration in remove().

> Jonathan
> 
>>
>> Thanks,
>> Yicong
>>
>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>>>   
>>>> ---  
>>>   
>>>> +
>>>> +static int hisi_ptt_register_pmu(struct hisi_ptt *hisi_ptt)
>>>> +{
>>>> +	u16 core_id, sicl_id;
>>>> +	char *pmu_name;
>>>> +	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;
>>>> +
>>>> +	return perf_pmu_register(&hisi_ptt->hisi_ptt_pmu, pmu_name, -1);  
>>>
>>> As below, you can put back the devm cleanup that you had in v4 now you
>>> have modified how the filter cleanup is done to also be devm managed.
>>>   
>>>> +}
>>>> +
>>>>  /*
>>>>   * The DMA of PTT trace can only use direct mapping, due to some
>>>>   * hardware restriction. Check whether there is an IOMMU or the
>>>> @@ -303,15 +825,32 @@ static int hisi_ptt_probe(struct pci_dev *pdev,
>>>>  
>>>>  	pci_set_master(pdev);
>>>>  
>>>> +	ret = hisi_ptt_register_irq(hisi_ptt);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>>  	ret = hisi_ptt_init_ctrls(hisi_ptt);
>>>>  	if (ret) {
>>>>  		pci_err(pdev, "failed to init controls, ret = %d.\n", ret);
>>>>  		return ret;
>>>>  	}
>>>>  
>>>> +	ret = hisi_ptt_register_pmu(hisi_ptt);
>>>> +	if (ret) {
>>>> +		pci_err(pdev, "failed to register pmu device, ret = %d", ret);
>>>> +		return ret;
>>>> +	}
>>>> +
>>>>  	return 0;
>>>>  }
>>>>  
>>>> +void hisi_ptt_remove(struct pci_dev *pdev)
>>>> +{
>>>> +	struct hisi_ptt *hisi_ptt = pci_get_drvdata(pdev);
>>>> +
>>>> +	perf_pmu_unregister(&hisi_ptt->hisi_ptt_pmu);  
>>>
>>> Now you have the filter cleanup occurring using a devm_add_action_or_reset()
>>> there is no need to have a manual cleanup of this - you can
>>> use the approach of a devm_add_action_or_reset like you had in v4.
>>>
>>> As it is the last call in the probe() order it will be the first one
>>> called in the device managed cleanup.
>>>   
>>>> +}
>>>> +  
>>>
>>>
>>> .
>>>   
> 
> .
>