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

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Message-ID: <871f22f4-c456-db15-3466-085971bd1221@gmail.com>
Date:   Sun, 23 Jul 2023 09:03:03 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     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: Fwd: PCI: Loongson: 8b3517f88ff2 breaks PCIe on some system

Hi,

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

Thanks.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217680

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