Re: [PATCH] PCI: cadence: skip the link polling when endpoint not connected

[Manivannan Sadhasivam]

On Tue, Jun 23, 2026 at 10:53:48AM +0530, Aksh Garg wrote:
> 
> 
> On 22/06/26 20:22, Manivannan Sadhasivam wrote:
> > On Fri, Jun 05, 2026 at 12:49:22PM +0530, Aksh Garg wrote:
> > > cdns_pcie_host_wait_for_link() polls on link-up for 10 retries with a
> > > delay of 90-100ms each (~1 second). A call to cdns_pcie_host_link_setup()
> > > during the resume operation blocks the resume operation unnecessarily for
> > > ~1s even when no endpoint device is connected.
> > > 
> > > Add skip_link_polling flag to track link state across suspend/resume
> > > cycles. If link was down before suspend, skip the expensive polling
> > > in resume since no endpoint was present.
> > > 
> > 
> > Won't you need the delay if a device gets plugged while the host was suspended?
> > We had this same concern with the DWC drivers and we left the delay as-is as
> > nothing prevents an user to connect a device when the host was suspended.
> 
> Yes, that is true. However, the platforms that do not support hot-plug can
> skip the delay during resume since no device could have been connected while
> suspended (only those platform's driver would be expected to set
> 'rc->skip_link_polling) just like what Tegra264 PCIe driver tries to do at
> [1], where the driver sets "pcie->link_up = false" if the link is down
> during the probe and if the controller doesn't support hot-plug.
> 

If the platform doesn't support hotplug, then it is perfectly fine to skip the
delay. But you need to name the flag as like 'no_hotplug' or something
relevant, not 'skip_link_polling'.

> Even if a user connects a device (when the host was suspended) to a platform
> which doesn't support hotplug, the user is expected to run a bus rescan,
> which doesn't call cdns_pcie_host_link_setup() anyway, hence the flag
> 'skip_link_polling' is not taken into account in that case.
> 

This is not about running the rescan, but about initializing the device. The 1s
delay in cdns_pcie_host_wait_for_link() is mandated by the PCIe spec after
starting LTSSM and before issuing the config read to the device. If this delay
is skipped and if a config read is issued to the device, then the device may not
respond and the failure may lead to PCI stack assuming that the device is dead.

- Mani

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