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

[Timothy Pearson <tpearson@raptorengineering.com>]

----- Original Message -----
> From: "Bjorn Helgaas" <helgaas@kernel.org>
> To: "Timothy Pearson" <tpearson@raptorengineering.com>
> Cc: "linuxppc-dev" <linuxppc-dev@lists.ozlabs.org>, "linux-kernel" <linux-kernel@vger.kernel.org>, "linux-pci"
> <linux-pci@vger.kernel.org>, "Madhavan Srinivasan" <maddy@linux.ibm.com>, "Michael Ellerman" <mpe@ellerman.id.au>,
> "christophe leroy" <christophe.leroy@csgroup.eu>, "Naveen N Rao" <naveen@kernel.org>, "Bjorn Helgaas"
> <bhelgaas@google.com>, "Shawn Anastasio" <sanastasio@raptorengineering.com>, "Lukas Wunner" <lukas@wunner.de>
> Sent: Wednesday, June 18, 2025 2:44:00 PM
> Subject: Re: [PATCH v2 2/6] pci/hotplug/pnv_php: Work around switches with broken

> [+cc Lukas, pciehp expert]
> 
> On Wed, Jun 18, 2025 at 11:56:54AM -0500, Timothy Pearson wrote:
>>  presence detection
> 
> (subject/commit wrapping seems to be on all of these patches)
> 
>> The Microsemi Switchtec PM8533 PFX 48xG3 [11f8:8533] PCIe switch system
>> was observed to incorrectly assert the Presence Detect Set bit in its
>> capabilities when tested on a Raptor Computing Systems Blackbird system,
>> resulting in the hot insert path never attempting a rescan of the bus
>> and any downstream devices not being re-detected.
> 
> Seems like this switch supports standard PCIe hotplug?  Quite a bit of
> this driver looks similar to things in pciehp.  Is there some reason
> we can't use pciehp directly?  Maybe pciehp could work if there were
> hooks for the PPC-specific bits?

While that is a good long term goal that Raptor is willing to work toward, it is non-trivial and will require buy-in from other stakeholders (e.g. IBM).  If practical, I'd like to get this series merged first, to fix the broken hotplug on our hardware that is deployed worldwide, then in parallel see what can be done to merge PowerNV support into pciehp.  Would that work?