Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver

From: Shuai Xue <xueshuai@linux.alibaba.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: will@kernel.org, Jonathan.Cameron@Huawei.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, rdunlap@infradead.org,
	robin.murphy@arm.com, mark.rutland@arm.com,
	baolin.wang@linux.alibaba.com, zhuo.song@linux.alibaba.com,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver
Date: Tue, 27 Sep 2022 14:01:24 +0800	[thread overview]
Message-ID: <63037753-af65-6229-95e9-72eb310069d7@linux.alibaba.com> (raw)
In-Reply-To: <20220923185141.GA1407035@bhelgaas>

在 2022/9/24 AM2:51, Bjorn Helgaas 写道:
> On Fri, Sep 23, 2022 at 10:46:09PM +0800, Shuai Xue wrote:
>> 在 2022/9/23 AM1:36, Bjorn Helgaas 写道:
>>> On Sat, Sep 17, 2022 at 08:10:35PM +0800, Shuai Xue wrote:
> 
>>>> +static struct device_attribute dwc_pcie_pmu_cpumask_attr =
>>>> +__ATTR(cpumask, 0444, dwc_pcie_pmu_cpumask_show, NULL);
>>>
>>> DEVICE_ATTR_RO()?
> 
>> DEVICE_ATTR_RO may a good choice. But does it fit the code style to use
>> DEVICE_ATTR_RO in drivers/perf? As far as know, CCN, CCI, SMMU,
>> qcom_l2_pmu use "struct device_attribute" directly.
> 
> DEVICE_ATTR_RO is just newer, and I think CCN, CCI, SMMU, etc. would
> be using it if they were written today.  Of course, the drivers/perf
> maintainers may have a different opinion :)

Well, you are right, I will use DEVICE_ATTR_RO instead :)

> 
>>> I think every caller of dwc_pcie_pmu_read_dword() makes the same check
>>> and prints the same message; maybe the message should be moved inside
>>> dwc_pcie_pmu_read_dword()?
>>>
>>> Same with dwc_pcie_pmu_write_dword(); moving the message there would
>>> simplify all callers.
>>
>> I would like to wrap dwc_pcie_pmu_{write}_dword out, use
>> pci_{read}_config_dword and drop the snaity check of return value as
>> Jonathan suggests.  How did you like it?
> 
> Sounds good.  Not sure the error checking is worthwhile since
> pci_read_config_dword() really doesn't return meaningful errors
> anyway.
> 
>>>> +static struct dwc_pcie_info_table *pmu_to_pcie_info(struct pmu *pmu)
>>>> +{
>>>> +	struct dwc_pcie_info_table *pcie_info;
>>>> +	struct dwc_pcie_pmu *pcie_pmu = to_pcie_pmu(pmu);
>>>> +
>>>> +	pcie_info = container_of(pcie_pmu, struct dwc_pcie_info_table, pcie_pmu);
>>>> +	if (pcie_info == NULL)
>>>> +		pci_err(pcie_info->pdev, "Can't get pcie info\n");
>>>
>>> It shouldn't be possible to get here for a pmu with no pcie_info, and
>>> callers don't check for a NULL pointer return value before
>>> dereferencing it, so I guess all this adds is an error message before
>>> a NULL pointer oops?  Not sure the code clutter is worth it.
>>
>> Do you mean to drop the snaity check of container_of?
> 
> Yes.  I'm suggesting that the NULL pointer oops itself has enough
> information to debug this problem, even without the pci_err().

I will drop the snaity check in next version.

Thank you for you valuable comments.

Best Regards,
Shuai

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