[PATCH] [v2] power/fsl: add MDIO dt binding for FMan

[Shaohui Xie]

Best Regards, 
Shaohui Xie


> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Tuesday, December 23, 2014 5:26 AM
> To: Medve Emilian-EMMEDVE1
> Cc: Xie Shaohui-B21989; linuxppc-dev at lists.ozlabs.org;
> devicetree at vger.kernel.org; Liberman Igal-B31950
> Subject: Re: [PATCH] [v2] power/fsl: add MDIO dt binding for FMan
> 
> On Mon, 2014-12-22 at 05:08 -0600, Emil Medve wrote:
> > Hello Scott,
> >
> >
> > On 12/22/2014 03:42 AM, Scott Wood wrote:
> > > On Mon, 2014-12-22 at 03:37 -0600, Emil Medve wrote:
> > >> Hello Scott,
> > >>
> > >>
> > >> On 12/22/2014 02:32 AM, Scott Wood wrote:
> > >>> On Mon, 2014-12-22 at 02:20 -0600, Emil Medve wrote:
> > >>>> For the purpose of an example in the binding document, I suggest
> > >>>> we just stick with the IEEE standard frequency.
> > >>>
> > >>> The whole reason for this property existing in the device tree is
> > >>> non-standard frequencies.
> > >>
> > >> While the standard claims 2.5 MHz, most MDIO controllers and PHY
> > >> devices support frequencies well beyond the standard. Specifying a
> > >> lower then the standard frequency for the benefit of some errata is
> > >> just one side of this property
> > >
> > > The erratum was (until now) the only claimed reason for it.  If
> > > there are other reasons why one would specify a different frequency
> > > (in particular, that relate to hardware description), please
> elaborate.
> >
> > From memory, the 1 Gb/s Vitesse PHY(s) we have on some of our DS
> > boards support 12.5 MHz. I can dig out more specs for specifics on
> > other PHY(s)
> >
> > 2.5 MHz is slow and even more so for high speed interfaces. With both
> > polling and interrupts (both MDIO and/or PHY) we've noticed (or
> > blamed) in the past some Ethernet performance issues on this very
> > slowness
> >
> > As of right now I'm not aware of another way to specify/coordinate the
> > MDC speed so setting a default (common denominator) in the DT that is
> > different then the IEEE standard seems ok
> >
> > >>>> We can continue this conversation about errata handling when we
> > >>>> submit the code relevant to this binding (and the FMan v3
> > >>>> support)
> > >>>
> > >>> It affects the binding, so let's discuss it now please.
> > >>
> > >> I think this specific (unpublished yet) errata has less bearing on
> > >> the binding then you might believe. This is mostly about providing
> > >> a common/default frequency supported by all the devices on some
> > >> board
> > >
> > > What reason other than an erratum would there be for the standard
> > > frequency not being supported?
> >
> > This is not about not supporting the standard frequency. This is about
> > the default frequency being different then the standard
> 
> OK, though rather than talk about defaults I'd phrase it as indicating
> that a higher frequency than standard is supported, or that a lower
> frequency than standard is required.
[S.H] below is the statement in v2:

+- bus-frequency
+		Usage: optional
+		Value type: <u32>
+		Definition: Specifies external MDIO bus clock speed which is
+		different from MDIO standard 2.5MHz. Should be defined for SoCs
+		on which the standard one cannot work.

What should I rephrase it? Replace the last sentence with "Should be defined
For SoCs on which a lower frequency than the standard is required."?

How about the value used in example?
Should 2.5MHz be used or a lower one?

Thanks!
Shaohui