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

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Date:   Thu, 30 Sep 2021 14:16:06 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Saravana Kannan <saravanak@...gle.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 9/30/21 1:14 PM, Saravana Kannan wrote:
> 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.

It is the same API that is being used whether you connect to the PHY at
ndo_open() time or whether you do that during the parent's ->probe()
fortunately or unfortunately. Now we could set a flag in either case,
and hope that it addresses both situations?

Being able to be selective about the Ethernet PHY driver is being used
is actually a good idea, there are plenty of systems out there whereby
using the Generic PHY driver will not lead to a functional Ethernet
link, if we could say "I want my dedicated driver, and not Generic PHY"
that would actually help some cases, too.
-- 
Florian