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

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Message-ID: <20250528223500.GA58129@bhelgaas>
Date: Wed, 28 May 2025 17:35:00 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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 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?