linux-kernel - Re: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings

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Message-Id: <52ec45eb-6633-4d51-96ff-d29d1743e1aa@app.fastmail.com>
Date:   Sun, 22 Oct 2023 14:36:13 +0100
From:   "Jiaxun Yang" <jiaxun.yang@...goat.com>
To:     "Linux regressions mailing list" <regressions@...ts.linux.dev>,
        "Manivannan Sadhasivam" <manivannan.sadhasivam@...aro.org>
Cc:     "Huacai Chen" <chenhuacai@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org,
        Krzysztof Wilczyński <kw@...ux.com>,
        "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings



在2023年10月20日十月 下午12:04，Thorsten Leemhuis写道：
> Hi, Thorsten here, the Linux kernel's regression tracker. Top-posting
> for once, to make this easily accessible to everyone.
>
> Just wondering what's up here. The patch this thread is about afaics was
> supposed to fix a regression reported in July
> (https://bugzilla.kernel.org/show_bug.cgi?id=217680 ), but has made not
> steps closer to get mainlined during the past few weeks. Is there a
> reason, or did it maybe fell through the cracks?
>
> Jiaxun Yang, from it quick look it seems like you wanted to post a v3,
> but never did so; but I might be mistaken there.

I just figure out the problem of this implementation.
Will resend and explain.

Thanks
- Jiaxun

>
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> --
> Everything you wanna know about Linux kernel regression tracking:
> https://linux-regtracking.leemhuis.info/about/#tldr
> If I did something stupid, please tell me, as explained on that page.
>
> #regzbot poke
>
> On 20.09.23 14:33, Linux regression tracking (Thorsten Leemhuis) wrote:
>> [CCing the regression list, as it should be in the loop for regressions:
>> https://docs.kernel.org/admin-guide/reporting-regressions.html]
>> 
>> On 07.09.23 07:08, Manivannan Sadhasivam wrote:
>>> On Thu, Sep 07, 2023 at 11:13:00AM +0800, Jiaxun Yang wrote:
>>>> 在 2023/9/7 9:18, Manivannan Sadhasivam 写道:
>>>> [...]
>>>>> Why do you need to walk through every single device instead of just bridges?
>>>>> I'm not the maintainer, but my suggestion is to go for Huacai Chen's solution.
>>>>
>>>> Thanks for your reply, unfortunately Huacai's solution is impractical in
>>>> this case.
>>>>
>>>> The problem we have, is firmware (or BIOS) setting improper MRRS for devices
>>>> attached under those bridges. So we have to fix up MRRS for every single
>>>> device.
>>>> We can't iterate child device in bridge quirk because there is no guarantee
>>>> that
>>>> bridge will be probed before  it's child device, partly due to hotplug.
>>>
>>> Okay, this clarifies and also warrants improvement in commit message.
>>>
>>> You could also use pci_walk_bus() after pci_host_probe() to iterate over the
>>> child devices under root bridge and set MRRS. IMO that would look neat.
>> 
>> Hi, Thorsten here, the Linux kernel's regression tracker. What's the
>> status here? The regression that was supposed to be fixed by the patched
>> that started this thread was reported 9 weeks ago[1] and the culprit
>> made it to many stable kernels as well. Would be really good to finally
>> fix this, as a regression like this should ideally be fixed within 2 to
>> 3 weeks (in both mainline and stable). With a revert if necessary -- is
>> this maybe still a option, or would that cause more trouble then it
>> solved (I guess that's the case).
>> 
>> [1] https://bugzilla.kernel.org/show_bug.cgi?id=217680
>> 
>> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
>> --
>> Everything you wanna know about Linux kernel regression tracking:
>> https://linux-regtracking.leemhuis.info/about/#tldr
>> If I did something stupid, please tell me, as explained on that page.
>> 
>>>> This quirk has been in tree for a while, until Huacai refactored it and
>>>> broke some
>>>> systems in 8b3517f88ff2 ("PCI: loongson: Prevent LS7A MRRS increases").
>>>>
>>>> Also to note that ks_pcie_quirk in drivers/pci/controller/dwc/pci-keystone.c
>>>> uses similar approach.
>>>>> This avoids iterating over bridges/devices two times.
>>>>>
>>>>> Also, please rename firmware to BIOS, as firmware commonly represents the
>>>>> software running on PCIe endpoint devices.
>>>> Ack, will fix in next reversion.
>>>>
>>>> Thanks
>>>> - Jiaxun
>>>>>
>>>>> - Mani
>>>> [...]
>>>

-- 
- Jiaxun