netdev - Re: phy address in the device tree, vs auto probing

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Message-Id: <20100210.113720.1026572228166328165.imp@bsdimp.com>
Date:	Wed, 10 Feb 2010 11:37:20 -0700 (MST)
From:	"M. Warner Losh" <imp@...imp.com>
To:	scottwood@...escale.com
Cc:	grant.likely@...retlab.ca, netdev@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, afleming@...escale.com
Subject: Re: phy address in the device tree, vs auto probing

In message: <4B72FAB2.5000804@...escale.com>
            Scott Wood <scottwood@...escale.com> writes:
: Grant Likely wrote:
: >> 1. What if we just don't specific a phy address with a reg property
: >> which would specify to auto probe it and find the phy as illustrated
: >> below?
: >>
: >>
: >>                Ethernet_MAC: ethernet@...00000 {
: >>                        #address-cells = <1>;
: >>                        #size-cells = <1>;
: >>                        phy-handle = <&phy0>;
: >>                        mdio {
: >>                                #address-cells = <1>;
: >>                                #size-cells = <0>;
: >>                                phy0: phy@7 {
: >>                                } ;
: >>                        } ;
: >>
: >> 2. Or a special value (-1 or something not 0 - 31) in the phy address
: >> that specifies to auto probe as illustrated below.
: >>                                phy0: phy@7 {
: >>                                        reg = <-1>;
: >>                                } ;
: > I don't like abusing the reg property in this way.  I wonder if a new
: > empty property would be a better way to indicate this.  Maybe
: > "phy-probe-address;"?  It would also be important to specify in the
: > binding that only one phy node is allowed when phy-probe-address is
: > used.
: > Also, without a known reg the 'phy@7' name is inaccurate.  Drop the
: > @7.
: > Scott, Andy: any thoughts?
: 
: I'm not fond of the -1.  I'd prefer the explicit phy-probe-address
: property, though I don't mind too much using the absence of reg.

There are times that you'd want a list of PHY addresses to use.  This
suggests a bitmask, but I don't know if they are common enough to
warrant the extra burden on the usual case...

Warner
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