netdev - Re: [PATCH pci] PCI: don't skip probing entire device if first fn OF node has status = "disabled"

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Date: Wed, 31 May 2023 02:15:09 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-pci@...r.kernel.org, netdev@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>,
	Claudiu Manoil <claudiu.manoil@....com>,
	Michael Walle <michael@...le.cc>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH pci] PCI: don't skip probing entire device if first fn OF
 node has status = "disabled"

On Tue, May 30, 2023 at 05:27:24PM -0500, Bjorn Helgaas wrote:
> Ah, you're right, sorry I missed that.  Dispensing with the SERDES
> details would make this more obvious.

Lesson learned. When I had just gotten out of college, every time I asked
the coworkers in my company what they're up to, I was amazed by them just
proceeding to tell me all the nitty gritty details of what they're doing
and debugging, like I was supposed to understand or care for that matter.
"Dude, can't you just paint the high level idea without using dorky words?"
Now I'm one of them...

> Not sure why this needs to change the pci_scan_slot() path, since
> Function 0 is present and enumerable even though it's not useful in
> some cases.

Well, the rationale for me was pretty simple: it's the pci_scan_slot() logic
that I want to change - continue enumeration in some cases when the pci_dev
for fn 0 is NULL - and I'm otherwise perfectly okay with pci_scan_slot()
getting a NULL pci_dev from pci_setup_device() for fn 0. That wasn't something
I had in mind to change.

This patch is what it takes to propagate a qualifier, without leaving a mark
in any structure, for that NULL return code: is it NULL because enumeration
came up with nothing, or is it NULL because pci_set_of_node() said so?

> Seems like something in pci_set_of_node() or a quirk could do whatever
> you need to do.

Could you help me out with a more detailed hint here? I'm not really
familiar with the PCI core code. You probably mean to suggest leaving a
stateful flag somewhere, though I'm not exactly sure where that is, that
would reach pci_scan_slot() enough to be able to alter its decision.