Re: [PATCH v5] PCI: dwc: Wait for link up only if link is started

[Ajay Agarwal <ajayagarwal@google.com>]

On Fri, Feb 14, 2025 at 03:12:55PM +0530, Manivannan Sadhasivam wrote:
> On Fri, Feb 14, 2025 at 10:18:27AM +0100, Johan Hovold wrote:
> > On Fri, Feb 14, 2025 at 02:45:03PM +0530, Ajay Agarwal wrote:
> > 
> > > Restarting this discussion for skipping the 1 sec of wait time if a
> > > certain platform does not necessarily wish or expect to bring the link
> > > up during probe time. I discussed with William and we think that a
> > > module parameter can be added which if true, would lead to the skipping
> > > of the wait time. By default, this parameter would be false, thereby
> > > ensuring that the current behaviour to wait for the link is maintained.
> > > 
> > > Please let me know if this is worth exploring.
> > 
> > No, module parameters are a thing of the past (except possibly in vendor
> > kernels). The default behaviour should just work.
> > 
> 
> +1
> 
> Btw, you need to come up with a valid argument for not enabling the link during
The argument for the link to not come up during probe is simply that the
product does not need the link to be up during probe. The requirement is
that the PCIe RC SW structures be prepared for link-up later, when there
is a trigger from the userspace or the vendor kernel driver.

I am looking to treat this like USB, say. The USB DWC could be probed when
the cable is not connected. That does not fail the probe. Later when the
cable is connected, the USB link comes up and the enumeration is
performed.

> probe. Also, not waiting for link during probe is also not going to work across
> all platforms where the controller is used, unless your hardware supports
> hotplug or LINK_UP IRQ.
We do not necessarily need the hotplug or LINK_UP IRQ right? Once the
LTSSM training is enabled using the triggers I mentioned above, I can
then wait for the link to come up using `dw_pcie_wait_for_link`. IOW,
polling for the link, which is what the `dw_pcie_host_init` does.

> 
> - Mani
> 
> -- 
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