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

[Manivannan Sadhasivam]

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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