linux-kernel - Re: Fwd: PCI: Loongson: 8b3517f88ff2 breaks PCIe on some system

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Message-ID: <d8471890-feb8-8953-a97d-5fc6b1f22d65@leemhuis.info>
Date:   Sun, 23 Jul 2023 13:13:04 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Bjorn Helgaas <bhelgaas@...gle.com>, jiaxun.yang@...goat.com,
        Aurelien Jarno <aurel32@...ian.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Loongarch <loongarch@...ts.linux.dev>
Subject: Re: Fwd: PCI: Loongson: 8b3517f88ff2 breaks PCIe on some system

On 23.07.23 04:03, Bagas Sanjaya wrote:
> 
> I notice a regression report on Bugzilla [1]. Quoting from it:
> 
>> After 8b3517f88ff2 ("PCI: loongson: Prevent LS7A MRRS increases") backported to stable, we have received multiple regression reports including one from Debian build farm[1] that some systems failed to initialize some PCIe devices.
>>
>> I was able to reproduce on one of my Loongson-3A4000+7A system. It seems like the root cause is firmware on those systems didn't set MRRS properly but 8b3517f88ff2 ("PCI: loongson: Prevent LS7A MRRS increases") assumed firmware's maximum MRRS is always valid.
>>
>> [1]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035587
> 
> See Bugzilla for the full thread.
> 
> The linked Debian BTS entry have debugging details on this regression
> (boot log, cpuinfo, and lspci).
> 
> Anyway, I'm adding this regression to regzbot:
> 
> #regzbot introduced: 8b3517f88ff298 https://bugzilla.kernel.org/show_bug.cgi?id=217680
> #regzbot title: LS7A MRRS quirk fails to initialize PCIe devices
> #regzbot link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035587

FWIW & TWIMC, a fix for this is in the works already afaics:

#regzbot monitor:
https://lore.kernel.org/all/20230718133259.2867432-1-jiaxun.yang@flygoat.com/
#regzbot fix: pci: loongson: Workaround MIPS firmware MRRS settings

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.