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

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Message-ID: <c9a99e29-1a16-4b46-8e3a-afd0aae5b76e@leemhuis.info>
Date:   Fri, 20 Oct 2023 13:04:05 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, linux-kernel@...r.kernel.org, kw@...ux.com,
        lpieralisi@...nel.org, stable@...r.kernel.org,
        Linux kernel regressions list <regressions@...ts.linux.dev>
Subject: Re: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings

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.

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
>>> [...]
>>