Re: [PATCH v2 19/27] pci: PCIe driver for Marvell Armada 370/XP systems

[Bjorn Helgaas <bhelgaas@google.com>]

On Wed, Jan 30, 2013 at 3:28 PM, Thomas Petazzoni
<thomas.petazzoni@free-electrons.com> wrote:
> Dear Bjorn Helgaas,
>
> On Wed, 30 Jan 2013 11:52:15 -0700, Bjorn Helgaas wrote:

>> It looks like your current system doesn't support trees below the
>> bridges, but hopefully we can make it so the generic enumeration
>> algorithms still work.
>
> In practice, in our situation, there isn't a tree below the bridge.
> There is one single device. I'd prefer to not implement features that I
> cannot effectively test, and let the implementation of those additional
> features to whoever will need them, and therefore be able to test them.

I understand the concern about testing, but my advice is to not use
that as an excuse to artificially limit the functionality of the code
you're writing :)

You're talking about emulating a bridge, and the bridge really doesn't
know or care what's downstream.  If it works with a single device
downstream, it should work with another bridge downstream.  Many
aspects of bridge configuration can be tested with creative
application of setpci, so that might be a possibility, too.

> I guess that if I integrate the PCI-to-PCI bridge emulation code within
> the Marvell driver, then I can keep it fairly limited to whatever the
> Marvell PCI driver requires, no?

Yeah, it's just that the pci_dev for this emulated bridge is used by
the generic PCI core code, e.g., pci_scan_bridge(), so whatever
emulation you do has to be robust enough that the core won't notice
it's emulated.

Bjorn