linux-kernel - 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 11:56:02 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
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 Wed, May 31, 2023 at 02:15:09AM +0300, Vladimir Oltean wrote:
> 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...

Haha :)  Communication is the hardest part!

> > 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.

What bad things happen without this patch?  I guess we enumerate
Function 0 but in some cases it's not useful?  That in itself wouldn't
be a disaster; there are lots of things we enumerate but don't use.
But in this case, maybe a driver would claim Function 0 but it
wouldn't work as expected?

Bjorn