linux-kernel - Re: [PATCH 1/2] net: dsa: felix: allow the device to be disabled

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Date:   Fri, 13 Mar 2020 00:07:37 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Michael Walle <michael@...le.cc>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>, devicetree@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Rob Herring <robh+dt@...nel.org>, Li Yang <leoyang.li@....com>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: [PATCH 1/2] net: dsa: felix: allow the device to be disabled

On Thu, 12 Mar 2020 at 23:45, Florian Fainelli <f.fainelli@...il.com> wrote:
>
> On 3/12/20 2:35 PM, Vladimir Oltean wrote:
> > On Thu, 12 Mar 2020 at 18:44, Michael Walle <michael@...le.cc> wrote:
> >>
> >> If there is no specific configuration of the felix switch in the device
> >> tree, but only the default configuration (ie. given by the SoCs dtsi
> >> file), the probe fails because no CPU port has been set. On the other
> >> hand you cannot set a default CPU port because that depends on the
> >> actual board using the switch.
> >>
> >> [    2.701300] DSA: tree 0 has no CPU port
> >> [    2.705167] mscc_felix 0000:00:00.5: Failed to register DSA switch: -22
> >> [    2.711844] mscc_felix: probe of 0000:00:00.5 failed with error -22
> >>
> >> Thus let the device tree disable this device entirely, like it is also
> >> done with the enetc driver of the same SoC.
> >>
> >> Signed-off-by: Michael Walle <michael@...le.cc>
> >> ---
> >>  drivers/net/dsa/ocelot/felix.c | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >> diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
> >> index 69546383a382..531c7710063f 100644
> >> --- a/drivers/net/dsa/ocelot/felix.c
> >> +++ b/drivers/net/dsa/ocelot/felix.c
> >> @@ -699,6 +699,11 @@ static int felix_pci_probe(struct pci_dev *pdev,
> >>         struct felix *felix;
> >>         int err;
> >>
> >> +       if (pdev->dev.of_node && !of_device_is_available(pdev->dev.of_node)) {
> >> +               dev_info(&pdev->dev, "device is disabled, skipping\n");
> >> +               return -ENODEV;
> >> +       }
> >> +
> >
> > IMHO since DSA is already dependent on device tree for PHY bindings,
> > it would make more sense to move this there:
>
> Michael's solution makes more sense, as this is a driver specific
> problem whereby you have a pci_dev instance that is created and does not
> honor the status property provided in Device Tree. If you were to look
> for a proper solution it would likely be within the PCI core actually.
>
> No other DSA switch has that problem because they use the
> I2C/SPI/platform_device/GPIO/whatever entry points into the driver model.

True, my problem with doing it in the PCI core is that "the book" [0]
doesn't actually say anything about the "status" property, so this
patch might get some pushback from the PCI maintainers (but I don't
actually know):

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 512cb4312ddd..50c2b3da134a 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2281,6 +2281,12 @@ static struct pci_dev *pci_scan_device(struct
pci_bus *bus, int devfn)

        pci_set_of_node(dev);

+       if (dev->dev.of_node && !of_device_is_available(dev->dev.of_node)) {
+               pci_bus_put(dev->bus);
+               kfree(dev);
+               return NULL;
+       }
+
        if (pci_setup_device(dev)) {
                pci_bus_put(dev->bus);
                kfree(dev);

OF bindings are completely optional with PCI, as you probably already
know. But there's nothing "driver" specific in disabling (i.e. not
probing) a device.

> --
>

[0] https://www.openfirmware.info/data/docs/bus.pci.pdf

Thanks,
-Vladimir