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

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Message-Id: <6FB48A2F-A8E9-4E1D-8052-568FB1E72643@exactco.de>
Date: Sat, 6 Dec 2025 11:14:05 +0100
From: René Rebe <rene@...ctco.de>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: glaubitz@...sik.fu-berlin.de,
 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

Hi,

> On 6. Dec 2025, at 02:07, Maciej W. Rozycki <macro@...am.me.uk> 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?"
> 
> Granted, the newest MIPS CPU/system controller (aka host bridge) I own is
> from 2013 and conventional PCI only, but that is just because the core was 
> synthesised for interfacing a conventional PCI base board I have the core 
> card plugged into.  Is it very old already or just somewhat old?
> 
> Chips continue being manufactured to date and I'm not sure as to new core
> designs, but those went through to at least 2018 and I'd expect some were 
> combined with PCIe system controller IP.
> 
> So this seems like something that needs to be keyed off perhaps the 
> capabilities of the system controller/host bridge?  If you give me a shell 
> recipe to trigger the issue you came across, then I can see what happens 
> with some of my MIPS systems.  I've got a bunch of options with PCI-PCIe 
> reverse bridges and PCIe switches I could try.

Just booting a kernel with or since a5fb3ff63287 ("PCI: Allow PCI bridges to go
to D3Hot on all non-x86”) should be enough. The systems that fail for me do
so instantly booting, usually earlier than later. e.g. when a storage, network or
system controller driver initializes.

Best,
	René

-- 
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