linux-kernel - Re: [PATCH 1/3] net: thunderx: Cleanup PHY probing code.

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Message-ID: <56E330E4.9090800@gmail.com>
Date:	Fri, 11 Mar 2016 12:56:04 -0800
From:	David Daney <ddaney.cavm@...il.com>
To:	Florian Fainelli <f.fainelli@...il.com>
CC:	Andrew Lunn <andrew@...n.ch>,
	David Daney <ddaney@...iumnetworks.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Robert Richter <rric@...nel.org>,
	Sunil Goutham <sgoutham@...ium.com>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Radha Mohan Chintakuntla <rchintakuntla@...ium.com>,
	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>
Subject: Re: [PATCH 1/3] net: thunderx: Cleanup PHY probing code.

On 03/11/2016 11:37 AM, Florian Fainelli wrote:
> On 11/03/16 11:06, Andrew Lunn wrote:
>>>> I don't see why it should wait around forever. I have boards with
>>>> Marvell PHYs, yet if i don't build the Marvell driver, the Ethernet
>>>> driver still loads, because the generic PHY driver is used instead.
>>>> Why does this not work here?
>>>
>>> As I said before, there is no driver for the device, so
>>> of_phy_find_device() will always return NULL.
>>
>> I'm not yet convinced this is true. I really do expect that the
>> generic PHY driver will bind to it. It might then go horribly wrong,
>> because it is not standard compliant, but that is a different issue.
>
> I concur with Andrew here, unless the PHY is guaranteed to return
> garbage when get_phy_id() is called, there is a good chance that the
> Generic PHY driver will be bound to this PHY device, or this is not
> happening for you for some reason?
>

get_phy_id() is working a designed.

For this phy, we have:

   compatible = "cortina,cs4223-slice";

Therefore get_phy_id() is being called with a is_c45 value of false.

get_phy_id() is returning a value of 0, which means that it succeeds, 
but the returned phy_id is 0xffffffff, which causes get_phy_device() to 
not create a phy_device, and no driver can be bound.

I know you are all skeptical, but I really think the best thing to do is 
not try to attach a phy driver when this compatible value is encountered.

It is a defective device tree, and I am attempting to handle it in the 
specific site where it can cause problems.

We are trying to distinguish between these two cases:

  - of_phy_find_device() returns NULL because driver is not yet bound

  - of_phy_find_device() returns NULL because "cortina,cs4223-slice"

I don't think we need to build some sort of frame work to handle things 
like this in a general way.

David Daney