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:   Sun, 4 Jun 2023 11:55:00 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Jianmin Lv <lvjianmin@...ngson.cn>
Cc:     Liu Peibao <liupeibao@...ngson.cn>,
        Bjorn Helgaas <helgaas@...nel.org>, 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,
        Binbin Zhou <zhoubinbin@...ngson.cn>,
        Huacai Chen <chenhuacai@...ngson.cn>
Subject: Re: [PATCH pci] PCI: don't skip probing entire device if first fn OF
 node has status = "disabled"

On Sat, Jun 03, 2023 at 10:35:50AM +0800, Jianmin Lv wrote:
> > How about 3. handle of_device_is_available() in the probe function of
> > the "loongson, pci-gmac" driver? Would that not work?
> > 
> This way does work only for the specified device. There are other devices,
> such as HDA, I2S, etc, which have shared pins. Then we have to add
> of_device_is_available() checking to those drivers one by one. And we are
> not sure if there are other devices in new generation chips in future. So
> I'm afraid that the way you mentioned is not suitable for us.

Got it, so you have more on-chip PCIe devices than the ones listed in
loongson64-2k1000.dtsi, and you don't want to describe them in the
device tree just to put status = "disabled" for those devices/functions
that you don't want Linux to use - although you could, and it wouldn't
be that hard or have unintended side effects.

Though you need to admit, in case you had an on-chip multi-function PCIe
device like the NXP ENETC, and you wanted Linux to not use function 0,
the strategy you're suggesting here that is acceptable for Loongson
would not have worked.

I believe we need a bit of coordination from PCIe and device tree
maintainers, to suggest what would be the encouraged best practices and
ways to solve this regression for the ENETC.