linux-kernel - Re: [PATCH v6 0/4] drivers/perf: add Synopsys DesignWare PCIe PMU driver support

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Message-ID: <375a0706-b76e-e8a8-cdac-ed628af6643c@linux.alibaba.com>
Date:   Mon, 31 Jul 2023 15:30:31 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Will Deacon <will@...nel.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        chengyou@...ux.alibaba.com, kaishen@...ux.alibaba.com,
        yangyicong@...wei.com, baolin.wang@...ux.alibaba.com,
        robin.murphy@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        rdunlap@...radead.org, mark.rutland@....com,
        zhuo.song@...ux.alibaba.com
Subject: Re: [PATCH v6 0/4] drivers/perf: add Synopsys DesignWare PCIe PMU
 driver support



On 2023/7/28 21:39, Will Deacon wrote:
> On Thu, Jul 27, 2023 at 11:45:22AM +0800, Shuai Xue wrote:
>>
>>
>> On 2023/7/26 04:59, Bjorn Helgaas wrote:
>>> On Mon, Jul 24, 2023 at 10:18:07AM +0100, Jonathan Cameron wrote:
>>>> On Mon, 24 Jul 2023 10:34:08 +0800
>>>> Shuai Xue <xueshuai@...ux.alibaba.com> wrote:
>>>>> On 2023/7/10 20:04, Shuai Xue wrote:
>>>>>> On 2023/6/16 16:39, Shuai Xue wrote:  
>>>>>>> On 2023/6/6 15:49, Shuai Xue wrote:  
>>>
>>>>>>>> This patchset adds the PCIe Performance Monitoring Unit (PMU) driver support
>>>>>>>> for T-Head Yitian 710 SoC chip. Yitian 710 is based on the Synopsys PCI Express
>>>>>>>> Core controller IP which provides statistics feature.
>>>
>>>> ...
>>>> Really a question for Bjorn I think, but here is my 2 cents...
>>>>
>>>> The problem here is that we need to do that fundamental redesign of the
>>>> way the PCI ports drivers work.  I'm not sure there is a path to merging
>>>> this until that is done.  The bigger problem is that I'm not sure anyone
>>>> is actively looking at that yet.  I'd like to look at this (as I have
>>>> the same problem for some other drivers), but it is behind various
>>>> other things on my todo list.
>>>>
>>>> Bjorn might be persuaded on a temporary solution, but that would come
>>>> with some maintenance problems, particularly when we try to do it
>>>> 'right' in the future.  Maybe adding another service driver would be
>>>> a stop gap as long as we know we won't keep doing so for ever. Not sure.
>>>
>>> I think the question here is around the for_each_pci_dev() in
>>> __dwc_pcie_pmu_probe()?  I don't *like* that because of the
>>> assumptions it breaks (autoload doesn't work, hotplug doesn't work),
>>> but:
>>>
>>>   - There are several other drivers that also do this,
>>>   - I don't have a better suggest for any of them,
>>>   - It's not a drivers/pci thing, so not really up to me anyway,
>>>
>>> so I don't have any problem with this being merged as-is, as long as
>>> you can live with the limitations.
>>>
>>> I don't think this series does anything to work around those
>>> limitations, i.e., it doesn't make up fake device IDs for module
>>> loading or fake events for hotplug, so it seems like we could improve
>>> the implementation later if we ever have a way to do it.
>>>
>>> Bjorn
>>
>> + Will
>>
>> Ok, thank you for confirmation, Bjorn. Then it comes to perf driver parts and
>> it is really a question for @Will I think.
>>
>> What's your opinion about merging this patch set, @Will?
> 
> No fundamental objection from me, but I'll have a closer look when you
> post a version addressing the feedback from Jonathan and Yicong.

Thanks for your input! I appreciate that you don't have any fundamental objections
to merging the patch set. I'll definitely take into account the feedback from Jonathan
and Yicong before posting a revised version.


Best Regards,
Cheers.
Shuai