linux-kernel - Re: [PATCH] PCI: Fix PCI bridges not to go to D3Hot on older RISC systems

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Message-Id: <A1DED1E0-BA75-466E-AEDA-6C56B8B163C3@exactco.de>
Date: Sat, 6 Dec 2025 11:02:51 +0100
From: René Rebe <rene@...ctco.de>
To: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>,
 linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 riccardo.mottola@...ero.it
Subject: Re: [PATCH] PCI: Fix PCI bridges not to go to D3Hot on older RISC
 systems

(Resent, was accidentally HTML before :-/)
Hey,

On 6. Dec 2025, at 09:31, John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de> wrote:
> 
> On Sat, 2025-12-06 at 01:07 +0000, Maciej W. Rozycki wrote:
>> On Tue, 2 Dec 2025, René Rebe wrote:
>> 
>>>> Is there actually a justification to restrict the use of D3 to ARM64,
>>>> PPC64 and RISCV? What about MIPS, LoongArch or s390x?
>>> 
>>> Because the ones I picked are more modern, and thus more likely to
>>> work. MIPS is very old. [...]
>> 
>> How old is "very old?"
> 
> I've got two desktop and one embedded Loongson MIPS systems at home (not LoongArch)
> and these are very recent (made in the 2020s). The desktop systems already come with
> PCI Express slots.

That’s great and all, but did you test a recent kernel since this PCI change I bisected
for sparc64?

I love my quirky Sgi MIPS64 Octane and O2 also very much, but fact is: those
systems had not only special proprietary high speed xbow interconnects, but also
very glitchy PCI bridges that already barely work to start with.

Also that just one modern Loongson system might work, does not mean all the
history of MIPS(64) system will be okay.

Just yesterday I found this change also breaking my HP PA-RISC C8000 [1] with:

BT Port failed to come ready!
BT_TRANSFER_INIT: B_BUSY failed to clear!

There was a reason given my experience keeping all CPU ISAs supported,
I had initially only chosen to allow modern ones. And again, they all where
not allowed to D3hot before, and only randomly allow listed since a5fb3ff63287
("PCI: Allow PCI bridges to go to D3Hot on all non-x86”), Mar 20 11:06:04 2025.

So we probably should update this to at least include HPPA until someone
finds time to further debug and patch this better.

That being said I did not yet found an issue on old x86 systems with the 2015
Year check removed to d3hot those more than mainline currently does.

Mit freundlichen Grüßen,
	René

[1] https://t2linux.com/hardware/desktop/HP/c8000/

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