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

[Aksh Garg]

On 23/06/26 11:15, Manivannan Sadhasivam wrote:
> 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'.

Sure, I will rename the flag to 'link_down_no_hotplug' to clarify that 
it tracks the link state when there's no hotplug support.

> > 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.

Understood, thanks for the explanation.

> - Mani