linux-kernel - Re: [PATCH V6] PCI: loongson: Skip scanning disabled child devices

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Message-ID: <CAL_JsqKae+Rw162G199zeN09GX+hjUiUxB9h+SN_PPKoeEmrug@mail.gmail.com>
Date:   Fri, 10 Feb 2023 10:49:49 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Liu Peibao <liupeibao@...ngson.cn>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        Jianmin Lv <lvjianmin@...ngson.cn>,
        Yinbo Zhu <zhuyinbo@...ngson.cn>,
        wanghongliang <wanghongliang@...ngson.cn>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6] PCI: loongson: Skip scanning disabled child devices

On Wed, Nov 16, 2022 at 8:09 PM Liu Peibao <liupeibao@...ngson.cn> wrote:
>
> Add a mechanism to disable on chip PCI devices by DT. Typically, when there
> are pins shareable between the platform device and the on chip PCI device,
> if the PCI device is not preferred, add `status = "disabled"` property to
> this PCI device DT node.
>
> For example, on LS2K1000, GMAC1 (on chip PCI device) and GPIO (platform
> device, not PCI device) 14 share the same pin. If GMAC1 is not preferred,
> add `status = "disabled"` property in GMAC1 DT node.
>
> Signed-off-by: Liu Peibao <liupeibao@...ngson.cn>
> ---
> V5 -> V6: 1. rewrite the commit log to make things clear.
>           2. replace "unavailable" as "disabled" in patch subject.
> V4 -> V5: clear the issue we are facing in commit log.
> V3 -> V4: 1. get rid of the masklist and search the status property
>           directly.
>           2. check the status property only when accessing the vendor ID.
> V2 -> V3: 1. use list_for_each_entry() for more clearly.
>           2. fix wrong use of sizeof().
> V1 -> V2: use existing property "status" instead of adding new property.
>
>  drivers/pci/controller/pci-loongson.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> index 05c50408f13b..efca0b3b5a29 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -194,6 +194,17 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus,
>                         return NULL;
>         }
>
> +#ifdef CONFIG_OF
> +       /* Don't access disabled devices. */
> +       if (pci_is_root_bus(bus) && where == PCI_VENDOR_ID) {
> +               struct device_node *dn;
> +
> +               dn = of_pci_find_child_device(bus->dev.of_node, devfn);
> +               if (dn && !of_device_is_available(dn))
> +                       return NULL;
> +       }
> +#endif

This should not be controller specific as a disabled node should be
honored on any platform. It also makes assumptions about how the PCI
scanning code works that PCI_VENDOR_ID read failing is enough to stop
scanning. Can you please test this patch I just sent[1].

Rob

[1] https://lore.kernel.org/all/20230210164351.2687475-1-robh@kernel.org/