linux-kernel - Re: [PATCH v3 2/3] driver core: fw_devlink: Add support for FWNODE_FLAG_NEEDS_CHILD_BOUND_ON

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Message-ID: <YUpIgTqyrDRXMUyC@lunn.ch>
Date:   Tue, 21 Sep 2021 23:02:57 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Len Brown <lenb@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Vladimir Oltean <olteanv@...il.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] driver core: fw_devlink: Add support for
 FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD

> There are cases where the children try to probe too quickly (before
> the parent has had time to set up all the resources it's setting up)
> and the child defers the probe. Even Andrew had an example of that
> with some ethernet driver where the deferred probe is attempted
> multiple times wasting time and then it eventually succeeds.

And i prefer an occasional EPROBE_DEFER over a broken Ethernet switch,
which is the current state. I'm happy to see optimisations, but not at
the expense of breaking working stuff.

> Also, this assumption that the child will be bound successfully upon
> addition forces the parent/child drivers to play initcall chicken

We have never had any initcall chicken problems. The switch drivers
all are standard mdio_module_driver, module_platform_driver,
module_i2c_driver, module_pci_driver. Nothing special here. Things
load in whatever order they load, and it all works out, maybe with an
EPROBE_DEFER cycle. Which is good, we get our error paths tested, and
sometimes find bugs that way.

     Andrew