[PATCH v2] PCI: dwc: Make Link Up IRQ logic handle already powered on PCIe switches

[Niklas Cassel]

Hello Krishna,

Currently:
For controllers with Link Up IRQ support, the pci_host_probe() call (which
will perform PCI Configuration Space reads) is done without any of the
delays mandated by the PCIe specification.

This seems quite bad.

A device might not be fully initialized during during the time of these
PCI Configuration Space reads, but might still return some bogus values
that are actually different from the Configuration Space reads if done
after respecting the delays mandated by the PCIe specification.

I think the options are:
1) Keep the pci_host_probe() call in dw_pcie_host_init() for controllers
   with Link Up IRQ support, but make sure that we respect the delays also
   in this case.
or
2) Remove the pci_host_probe() call from dw_pcie_host_init(), and make sure
   that pci_host_probe() is done by the first Link Up IRQ
   (i.e. what this patch does).


One big thing with using the Link Up IRQ is to not do any delay during PCIe
controller driver's probe(), which reduces startup time, exactly as your
commit message in commit 36971d6c5a9a ("PCI: qcom: Don't wait for link if
we can detect Link Up") explains.
Therefore, I don't think that 1) is a good solution, so that leaves us with
2).


If pwrctrl drivers are created as part of the pci_host_probe() call,
I think that perhaps an alternative would be to create an explict
pwrctrl_init() function, and let the PCI controller drivers that actually
use pwrctrl call that from their probe().
(And just remove the same from pci_host_probe() ?)

In fact, looking at your suggested patches (that hasn't landed yet):
[PATCH 3/5] PCI/pwrctrl: Add APIs for explicitly creating and destroying pwrctrl devices
[PATCH 5/5] PCI/pwrctrl: Switch to the new pwrctrl APIs

https://lore.kernel.org/linux-pci/20251124-pci-pwrctrl-rework-v1-5-78a72627683d@oss.qualcomm.com/
https://lore.kernel.org/linux-pci/20251124-pci-pwrctrl-rework-v1-3-78a72627683d@oss.qualcomm.com/

Seem to do exactly that:
Call pci_pwrctrl_create_devices() explicitly from the PCIe controller drivers
directly, and removes the pci_pwrctrl_create_device() call from pci_host_probe().

So I don't really understand your concern with this series, at least not if
it goes on top of your series:
https://lore.kernel.org/linux-pci/20251124-pci-pwrctrl-rework-v1-0-78a72627683d@oss.qualcomm.com/


Kind regards,
Niklas