linux-kernel - Re: [PATCH 3/3] ARM: zynq: DT: Add Ethernet phys

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Date:	Fri, 29 Aug 2014 11:23:57 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Sören Brinkmann 
	<soren.brinkmann@...inx.com>
CC:	Andreas Färber <afaerber@...e.de>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] ARM: zynq: DT: Add Ethernet phys

On 08/29/2014 10:31 AM, Jason Gunthorpe wrote:
> On Fri, Aug 29, 2014 at 08:35:36AM -0700, Sören Brinkmann wrote:
> 
>> The compatible string is listed as optional property for PHYs. So, not
>> having one is an option, I guess. But, I'd also prefer to at least keep
>> the -c22 one, since I saw problems when I tried using -c45 (the Zed phy
>> should support it...).
> 
> -c45 and -c22 use a completely different MDIO protocol, Zed doesn't
> have a 10GE port, so it certainly doesn't use -c45.

Most recent 1GbE PHYs should also implement clause 45. It is a nice
improvement if you are using lot of transactions, otherwise clause 45
over clause 22 is suitable and supported by the PHY library (for EEE in
particular).

> 
> If there is no compatible string at all the defined default is to use
> -c22.

Absolutely, the current binding makes that property optional, but I
think we should make it mandatory instead.

> 
>> Also, so far, we haven't had any phy nodes in our Zynq dts files and
>> Ethernet worked, so the auto-detection there works pretty well
>> apparently. But it may be problematic if more than a single PHY is on
>> the MDIO bus, I'd assume.
> 
> Phy autodetection has always worked in some cases, but for DT ethernet
> bindings it is expected that there is an option to specify an explicit
> MDIO bus, and a phy-handle phandle to point to the phy. The phy should
> be explicitly called out with the fixed MDIO address specified to
> avoid sketchy MDIO address auto probing.
> 
> This provides the framework to specify interrupts and register
> overrides for the phy in the DT.

Absolutely, on the plus side, avoiding auto-detection also allows you to
have a shorter boot time (usually by a factor of few hundreds of msecs
depending on how the MDIO buses handle errors).
--
Florian
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