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

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Date:   Tue, 21 Sep 2021 18:00:26 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Andrew Lunn <andrew@...n.ch>
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

On Tue, Sep 21, 2021 at 5:45 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > Wait, what's the difference between a real fix vs a long term fix? To
> > me those are the same.
>
> Maybe the long term fix is you follow the phandle to the actual
> resources, see it is present, and allow the probe? That brings you in
> line with how things actually work with devices probing against
> resources.
>
> I don't know how much work that is, since there is no uniform API to
> follow a phandle to a resource. I think each phandle type has its own
> helper. For an interrupt phandle you need to use of_irq_get(), for a
> gpio phandle maybe of_get_named_gpio_flags(), for a reset phandle
> __of_reset_control_get(), etc.

That goes back to Rafael's reply (and I agree):

"Also if the probe has already started, it may still return
-EPROBE_DEFER at any time in theory, so as a rule the dependency is
actually known to be satisfied when the probe has successfully
completed."

So waiting for the probe to finish is the right behavior/intentional
for fw_devlink.

> Because this does not sounds too simple, maybe you can find something
> simpler which is a real fix for now, good enough that it will get
> merged, and then you can implement this phandle following for the long
> term fix?

The simpler fix is really just this patch. I'm hoping Greg/Rafael see
my point about doing the exception this way prevents things from
getting worse will we address existing cases that need the flag.

The long/proper fix is to the DSA framework. I have some ideas that I
think will work but I've had time to get to (but on the top of my
upstream work list). We can judge that after I send out the patches :)

-Saravana