linux-kernel - Re: [PATCH v2 2/6] pci/hotplug/pnv_php: Work around switches with broken

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Message-ID: <aFUTV87SMdpHRbt8@wunner.de>
Date: Fri, 20 Jun 2025 09:52:55 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Timothy Pearson <tpearson@...torengineering.com>
Cc: Bjorn Helgaas <helgaas@...nel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...r.kernel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	christophe leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Shawn Anastasio <sanastasio@...torengineering.com>
Subject: Re: [PATCH v2 2/6] pci/hotplug/pnv_php: Work around switches with
 broken

On Thu, Jun 19, 2025 at 02:29:33PM -0500, Timothy Pearson wrote:
> To be perfectly frank the existing code quality in this driver
> (and the associated EEH driver) is not the best, and it's been
> a frustrating experience trying to hack it into semi-stable
> operation.
> 
> I would vastly prefer to rewrite / integrate into the pciehp driver,
> and we have plans to do so, but that will take an unacceptable amount
> of time vs. trying to fix up the existing driver as a stopgap.
> 
> As you mentioned, pciehp already has this fix, so we just have to
> deal with the duplicated code until we (Raptor) figures out how to
> merge PowerNV support into pciehp.

I don't know how much PCIe hotplug on PowerNV differs from native,
spec-compliant PCIe hotplug.  If the differences are vast (and I
get the feeling they might be if I read terms like "PHB" and
"EEH unfreeze", which sound completely foreign to me), it might
be easier to refactor pnv_php.c and copy patterns or code from
pciehp, than to integrate the functionality from pnv_php.c into
pciehp.

pciehp does carry some historic baggage of its own (such as poll mode),
which you may not want to deal with on PowerNV.

One thing I don't quite understand is, it sounds like you've
attached a PCIe switch to a Root Port and the hotplug ports
are on the PCIe switch.  Aren't those hotplug ports just
bog-standard ones that can be driven by pciehp?  My expectation
would have been that a PowerNV-specific hotplug driver would
only be necessary for hotplug-capable Root Ports.

Thanks,

Lukas