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

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Date:   Thu, 30 Sep 2021 13:14:37 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vivien Didelot <vivien.didelot@...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, Sep 30, 2021 at 1:06 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
> On 9/30/21 12:48 PM, Saravana Kannan wrote:
> > On Thu, Sep 30, 2021 at 12:38 PM Andrew Lunn <andrew@...n.ch> wrote:
> >>
> >>> Btw, do we have non-DSA networking devices where fw_devlink=on
> >>> delaying PHY probes is causing an issue?
> >>
> >> I don't know if issues have been reported, but the realtek driver has
> >> had problems in the past when the generic driver is used. Take a look
> >> at r8169_mdio_register(), it does something similar to DSA.
> >
> > Does it have the issue of having the PHY as its child too and then
> > depending on it to bind to a driver? I can't tell because I didn't
> > know how to find that info for a PCI device.
>
> Yes, r8169 includes a MDIO bus controller, and the PHY is internal to
> the Ethernet MAC. These are AFAIR the relevant changes to this discussion:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=16983507742cbcaa5592af530872a82e82fb9c51
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=11287b693d03830010356339e4ceddf47dee34fa
>
>
> >
> >>
> >> What is going to make things interesting is that phy_attach_direct()
> >> is called in two different contexts. During the MAC drivers probe, it
> >> is O.K. to return EPROBE_DEFER, and let the MAC driver try again
> >> later, if we know there is a specific PHY driver for it. But when
> >> called during the MAC drivers open() op, -EPROBE_DEFER is not
> >> allowed. What to do then is an interesting question.
> >
> > Yeah, basically before doing an open() it'll have to call an API to
> > say "just bind with whatever you got". Or something along those lines.
> > I already know how to get that to work. I'll send some RFC soonish (I
> > hope).
>
> I don't think this is going to scale, we have dozens and dozens of
> drivers that connect to the PHY during ndo_open().

Whichever code calls ->ndo_open() can't that mark all the PHYs that'll
be used as "needs to be ready now"? In any case, if we can have an API
that allows a less greedy Generic PHY binding, we could slowly
transition drivers over or at least move them over as they hit issues
with Gen PHY. Anyway, I'll think discussing it over code would be
easier. I'll also have more context as I try to make changes. So,
let's continue this on my future RFC.

-Saravana

> It is not realistic
> to audit them all, just like the opposite case where the drivers do
> probe MDIO/PHY during their .probe() call is not realistic either.
> --
> Florian