linux-kernel - Re: [PATCH 2/3] pci/hotplug/pnv_php: Work around switches with broken presence detection

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Message-ID: <Z_nskClPmT4A_5Cf@wunner.de>
Date: Sat, 12 Apr 2025 06:31:12 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Shawn Anastasio <sanastasio@...torengineering.com>
Cc: linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, tpearson@...torengineering.com,
	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>,
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: Re: [PATCH 2/3] pci/hotplug/pnv_php: Work around switches with
 broken presence detection

On Fri, Apr 04, 2025 at 06:42:32AM +0200, Lukas Wunner wrote:
> On Thu, Apr 03, 2025 at 11:18:09PM -0500, Shawn Anastasio wrote:
> > 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.
> > 
> > Work around this by additionally checking whether the PCIe data link is
> > active or not when performing presence detection on downstream switches'
> > ports, similar to the pciehp_hpc.c driver.
> [...]
> > --- a/drivers/pci/hotplug/pnv_php.c
> > +++ b/drivers/pci/hotplug/pnv_php.c
> > @@ -390,6 +390,20 @@ static int pnv_php_get_power_state(struct hotplug_slot *slot, u8 *state)
> >  	return 0;
> >  }
> >  
> > +static int pcie_check_link_active(struct pci_dev *pdev)
> > +{
> > +	u16 lnk_status;
> > +	int ret;
> > +
> > +	ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
> > +	if (ret == PCIBIOS_DEVICE_NOT_FOUND || PCI_POSSIBLE_ERROR(lnk_status))
> > +		return -ENODEV;
> > +
> > +	ret = !!(lnk_status & PCI_EXP_LNKSTA_DLLLA);
> > +
> > +	return ret;
> > +}
> > +
> 
> This appears to be a 1:1 copy of pciehp_check_link_active(),
> save for the ctrl_dbg() call.
> 
> For the sake of code-reuse, please move the function into the
> PCI library drivers/pci/pci.c so that it can be used everywhere.
> 
> Note that there's another patch pending which does exactly that:
> 
> https://lore.kernel.org/r/20250225-qps615_v4_1-v4-7-e08633a7bdf8@oss.qualcomm.com/
> 
> So either include that patch in your series (addressing the review
> feedback I sent for it and cc'ing the original submitter) or wait
> for it to be respun by the original submitter.

Update -- Krishna respun the patch:

https://lore.kernel.org/r/20250412-qps615_v4_1-v5-7-5b6a06132fec@oss.qualcomm.com/