Re: [PATCH] PCI: controller: dwc: Make PCI_IMX6 depend on PCIEPORTBUS

[Trent Piepho <tpiepho@impinj.com>]

On Thu, 2018-12-06 at 11:28 +0100, Lucas Stach wrote:
> Am Mittwoch, den 05.12.2018, 23:45 -0800 schrieb Andrey Smirnov:
> > Building a kernel with CONFIG_PCI_IMX6=y, but CONFIG_PCIEPORTBUS=n
> > produces a system where built-in PCIE bridge (16c3:abcd) isn't
> > bound
> > to pcieport driver. This, in turn, results in a PCIE bus that is
> > capable of enumerating attached PCIE device, but lacks functional
> > interrupt support.
> 
> This is odd. AFAIK PCI port services are a totally optional thing and
> them being absent should not lead to a non-functional PCI bus. So I
> would really like to see some deeper analysis what is going on here.

I noticed this previously, 
https://www.spinics.net/lists/linux-pci/msg77840.html

What happened was that PCIEPORTBUS *was* selected by all the platform
dwc drivers and those selections were removed in:

commit f3fdfc4ac3a26865e84627a7fe08a906081e5abc
Author: Bjorn Helgaas <bhelgaas@google.com>
Date:   Fri May 18 15:08:36 2018 -0500

    PCI: Remove host driver Kconfig selection of CONFIG_PCIEPORTBUS
    
    Host bridge drivers do not use the portdrv interfaces (struct pcie_device,
    struct pcie_port_service_driver, pcie_port_service_register(), etc), and
    they should not select CONFIG_PCIEPORTBUS.

I encountered this when a kernel defconfig that previously turned on
PCIEPORTBUS stopped turning in on, resulting in the situation that
Andrey describes:  no errors, device present, but no MSI interrupts.

The in kernel defconfigs (mine not being one of those) for all the dwc
pcie users should probably be refreshed to enable pcieportbus.

It seems appropriate that the port services are optional and it's
unfortunate that the kernel defconfig system resolves in the change in
this manner, vs keeping pcieportbus on by default.  I do know why it is
this way and I don't think there is any great solution there.

It has never been clear to me why pcieportbus was necessary for MSI.