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

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Message-ID: <634f4762-cf2e-4535-f369-4032d65093f0@linux.alibaba.com>
Date:   Thu, 27 Jul 2023 11:45:22 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Will Deacon <will@...nel.org>
Cc:     chengyou@...ux.alibaba.com, kaishen@...ux.alibaba.com,
        yangyicong@...wei.com, will@...nel.org,
        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 2023/7/26 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?

Best Regards,
Shuai