linux-kernel - Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN

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Date:   Thu, 26 Aug 2021 16:44:58 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Len Brown <lenb@...nel.org>,
        Alvin Sipraga <ALSI@...g-olufsen.dk>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT

On Thu, Aug 26, 2021 at 1:53 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > The  DT node in [2] is probed by realtek_smi_probe() [3]. The call flow is:
> > realtek_smi_probe()
> >   -> dsa_register_switch()
> >     -> dsa_switch_probe()
> >       -> dsa_tree_setup()
> >         -> dsa_tree_setup_switches()
> >           -> dsa_switch_setup()
> >             -> ds->ops->setup(ds)
> >               -> rtl8366rb_setup()
> >                 -> realtek_smi_setup_mdio()
> >                   -> of_mdiobus_register()
> >                      This scans the MDIO bus/DT and device_add()s the PHYs
> >           -> dsa_port_setup()
> >             -> dsa_port_link_register_of()
> >               -> dsa_port_phylink_register()
> >                 -> phylink_of_phy_connect()
> >                   -> phylink_fwnode_phy_connect()
> >                     -> phy_attach_direct()
> >                        This checks if PHY device has already probed (by
> >                        checking for dev->driver). If not, it forces the
> >                        probe of the PHY using one of the generic PHY
> >                        drivers.
> >
> > So within dsa_register_switch() the PHY device is added and then
> > expected to have probed in the same thread/calling context. As stated
> > earlier, this is not guaranteed by the driver core.
>
> Have you looked at:
>
> commit 16983507742cbcaa5592af530872a82e82fb9c51
> Author: Heiner Kallweit <hkallweit1@...il.com>
> Date:   Fri Mar 27 01:00:22 2020 +0100
>
>     net: phy: probe PHY drivers synchronously
>
> See the full commit message, but the code change is:
>
> iff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 3b8f6b0b47b5..d543df282365 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -2577,6 +2577,7 @@ int phy_driver_register(struct phy_driver *new_driver, struct module *owner)
>         new_driver->mdiodrv.driver.probe = phy_probe;
>         new_driver->mdiodrv.driver.remove = phy_remove;
>         new_driver->mdiodrv.driver.owner = owner;
> +       new_driver->mdiodrv.driver.probe_type = PROBE_FORCE_SYNCHRONOUS;
>
>         retval = driver_register(&new_driver->mdiodrv.driver);
>         if (retval) {
>
> How does this add to the overall picture?

Doesn't add much to the discussion. In the example I gave, the driver
already does synchronous probing. If the device can't probe
successfully because a supplier isn't ready, it doesn't matter if it's
a synchronous probe. The probe would still be deferred and we'll hit
the same issue. Even in the situation the commit [5] describes, if
parallelized probing is done and the PHY depended on something (say a
clock), you'd still end up not probing the PHY even if the driver is
present and the generic PHY would end up force probing it.

[5] - https://lore.kernel.org/netdev/612b81d5-c4c1-5e20-a667-893eeeef0bf5@gmail.com/

-Saravana