linux-kernel - Re: [PATCH v4 4/5] PCI: host-common: Add link down handling for host bridges

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Message-ID: <fr6orvqq62hozn5g3svpyyazdshv4kh4xszchxbmpdcpgp5pg6@mlehmlasbvrm>
Date: Fri, 30 May 2025 09:16:59 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, 
	Oliver O'Halloran <oohall@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Zhou Wang <wangzhou1@...ilicon.com>, 
	Will Deacon <will@...nel.org>, Robert Richter <rric@...nel.org>, 
	Alyssa Rosenzweig <alyssa@...enzweig.io>, Marc Zyngier <maz@...nel.org>, 
	Conor Dooley <conor.dooley@...rochip.com>, Daire McNamara <daire.mcnamara@...rochip.com>, 
	dingwei@...vell.com, cassel@...nel.org, Lukas Wunner <lukas@...ner.de>, 
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, linuxppc-dev@...ts.ozlabs.org, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 4/5] PCI: host-common: Add link down handling for host
 bridges

On Wed, May 28, 2025 at 05:35:00PM -0500, Bjorn Helgaas wrote:
> On Thu, May 08, 2025 at 12:40:33PM +0530, Manivannan Sadhasivam wrote:
> > The PCI link, when down, needs to be recovered to bring it back. But that
> > cannot be done in a generic way as link recovery procedure is specific to
> > host bridges. So add a new API pci_host_handle_link_down() that could be
> > called by the host bridge drivers when the link goes down.
> > 
> > The API will iterate through all the slots and calls the pcie_do_recovery()
> > function with 'pci_channel_io_frozen' as the state. This will result in the
> > execution of the AER Fatal error handling code. Since the link down
> > recovery is pretty much the same as AER Fatal error handling,
> > pcie_do_recovery() helper is reused here. First the AER error_detected
> > callback will be triggered for the bridge and the downstream devices. Then,
> > pci_host_reset_slot() will be called for the slot, which will reset the
> > slot using 'reset_slot' callback to recover the link. Once that's done,
> > resume message will be broadcasted to the bridge and the downstream devices
> > indicating successful link recovery.
> 
> Link down is an event for a single Root Port.  Why would we iterate
> through all the Root Ports if the link went down for one of them?

Because on the reference platform (Qcom), link down notification is not
per-port, but per controller. So that's why we are iterating through all ports.
The callback is supposed to identify the ports that triggered the link down
event and recover them.

- Mani

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