Re: [PATCH] DT: add MDIO node for FMan node

[Scott Wood <scottwood-KZfg59tc24xl57MIdRCFDg@public.gmane.org>]

On Thu, 2014-11-13 at 02:02 -0600, Xie Shaohui-B21989 wrote:
> 
> 
> Best Regards, 
> Shaohui Xie
> 
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Thursday, November 13, 2014 3:15 PM
> > To: Xie Shaohui-B21989
> > Cc: Liberman Igal-B31950; linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org;
> > devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Medve Emilian-EMMEDVE1
> > Subject: Re: [PATCH] DT: add MDIO node for FMan node
> > 
> > On Thu, 2014-11-13 at 01:11 -0600, Xie Shaohui-B21989 wrote:
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Thursday, November 13, 2014 2:17 PM
> > > > To: Xie Shaohui-B21989
> > > > Cc: Liberman Igal-B31950; linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org;
> > > > devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Medve Emilian-EMMEDVE1
> > > > Subject: Re: [PATCH] DT: add MDIO node for FMan node
> > > >
> > > > On Wed, 2014-11-12 at 07:40 -0600, Xie Shaohui-B21989 wrote:
> > > > > > -----Original Message-----
> > > > > > From: Wood Scott-B07421
> > > > > > Sent: Wednesday, November 12, 2014 1:38 AM
> > > > > > To: Xie Shaohui-B21989
> > > > > > Cc: Liberman Igal-B31950; linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org;
> > > > > > devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Medve Emilian-EMMEDVE1
> > > > > > Subject: Re: [PATCH] DT: add MDIO node for FMan node
> > > > > >
> > > > > > On Tue, 2014-11-11 at 04:32 -0600, Xie Shaohui-B21989 wrote:
> > > > > > > > -----Original Message-----
> > > > > > > > From: Wood Scott-B07421
> > > > > > > > Sent: Tuesday, November 11, 2014 8:23 AM
> > > > > > > > To: shh.xie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> > > > > > > > Cc: linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org;
> > > > > > > > devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Medve Emilian-EMMEDVE1; Xie
> > > > > > > > Shaohui-B21989
> > > > > > > > Subject: Re: [PATCH] DT: add MDIO node for FMan node
> > > > > > > >
> > > > > > > > On Tue, 2014-11-04 at 19:56 +0800, shh.xie-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> > > > > > > > > From: Shaohui Xie <Shaohui.Xie-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > > > > > > > >
> > > > > > > > > This binding is for FMan MDIO, it covers FMan v2 & FMan v3.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Shaohui Xie <Shaohui.Xie-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > > > > > > > > ---
> > > > > > > > > based on http://patchwork.ozlabs.org/patch/390351/
> > > > > > > > > for 'next' of
> > > > > > > > >
> > git://git.kernel.org/pub/scm/linux/kernel/git/scottwood/linux.
> > > > > > > > > git
> > > > > > > >
> > > > > > > > Are there any other FMan pieces that are missing from the
> > > > > > > > above
> > > > patch?
> > > > > > > [S.H] I'm adding Igal for this comment.
> > > > > > >
> > > > > > > >
> > > > > > > > > +- bus-frequency
> > > > > > > > > +		Usage: optional
> > > > > > > > > +		Value type: <u32>
> > > > > > > > > +		Definition: Default MDIO bus clock speed.
> > > > > > > >
> > > > > > > > Use clocks/clock-names
> > > > > > > [S.H] The MDIO uses Fman clock and divides it to a proper
> > > > > > > value which
> > > > > > is specified by this property.
> > > > > >
> > > > > > Use clocks/clock-names to describe that relationship.
> > > > > >
> > > > >
> > > > > [S.H] The MDIO node is sub-node and embedded in Fman node, the
> > > > > clocks/clock-names is provided by Fman node, should repeat them in
> > > > > MDIO node? For the default MDIO bus clock speed, maybe "clock-
> > ranges"
> > > > > should be used?
> > > >
> > > > It's a different clock.  You wouldn't be repeating.  If it's derived
> > > > from the FMan clock, then maybe you don't need anything here (does
> > > > the driver know what the divider is, or would that need to be
> > > > specified in the device tree?), but no more clock-frequency/bus-
> > frequency properties.
> > > >
> > > [S.H] The purpose here is to get a specific clock frequency, driver to
> > use it to calculate the divider.
> > > Then the Fman clock can be divided to the frequency.
> > 
> > Oh, so this is stating a desired frequency and not something that already
> > exists?  What determines this frequency?  Is it based on board design, or
> > just on the MDIO standard, etc?  I'm wondering if the device tree is the
> > right place for it.
> [S.H] Yes, a desired frequency which is different with MDIO standard.

I'm not sure what you mean by "different with".  Do you mean "different
from"?  What does the standard say about frequency?

> The Fman clock and the divider determines this frequency.
> Since Fman clock is different on different SoCs, so specify the desired frequency, 
> then to get the proper divider.

Why does the fman clock being different mean the mdio clock should be
different?

-Scott


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