linux-kernel - Re: [PATCH 19/22] dt/bindings: add micrel,rmii_ref_clk_sel_25

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Message-ID: <20141112091920.GC15215@localhost>
Date:	Wed, 12 Nov 2014 10:19:20 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Johan Hovold <johan@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Florian Fainelli <f.fainelli@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 19/22] dt/bindings: add micrel,rmii_ref_clk_sel_25_mhz to
 eth-phy binding

On Wed, Nov 12, 2014 at 08:01:27AM +0100, Sascha Hauer wrote:
> On Tue, Nov 11, 2014 at 07:18:25PM +0100, Johan Hovold wrote:
> > On Tue, Nov 11, 2014 at 05:57:42PM +0000, Mark Rutland wrote:
> > > On Tue, Nov 11, 2014 at 05:37:37PM +0000, Johan Hovold wrote:
> > > > Add "micrel,rmii_ref_clk_sel_25_mhz" to Micrel ethernet PHY binding
> > > > documentation.
> > > > 
> > > > Cc: devicetree@...r.kernel.org
> > > > Signed-off-by: Johan Hovold <johan@...nel.org>
> > > > ---
> > > >  Documentation/devicetree/bindings/net/micrel.txt | 5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/net/micrel.txt b/Documentation/devicetree/bindings/net/micrel.txt
> > > > index a1bab5eaae02..9b08dd6551dd 100644
> > > > --- a/Documentation/devicetree/bindings/net/micrel.txt
> > > > +++ b/Documentation/devicetree/bindings/net/micrel.txt
> > > > @@ -19,6 +19,11 @@ Optional properties:
> > > >  
> > > >                See the respective PHY datasheet for the mode values.
> > > >  
> > > > + - micrel,rmii_ref_clk_sel_25_mhz: rmii_ref_clk_sel bit selects 25 MHz mode
> > > > +
> > > > +		Whether 25 MHz (rather than 50 Mhz) clock mode is selected
> > > > +		when the rmii_ref_clk_sel bit is set.
> > > 
> > > s/_/-/ in property names please.
> > 
> > Ouch, copied from variable name, sorry.
> > 
> > > That said, I don't follow the meaning. Does this cause the kernel to do
> > > something different, or is is simply that a 25MHz ref clock is wired up?
> > 
> > Yes, the driver currently sets this configuration bit based on a common
> > clock binding.
> > 
> > However, it turns out the meaning of the bit is reversed on some PHY
> > variants. On most PHYs 50 MHz mode is selected by setting this bit,
> > whereas on the PHYs that need this new property, setting it selects 25
> > MHz mode instead.
> 
> Maybe rename the property to something like rmii-ref-clk-25mhz-active-high
> then? Also you should probably make it more explicit that this is a
> hardware property and not for adjusting the clock.

You're right, but how about calling it

	micrel,rmii-reference-clock-select-inverted

Then no one will set it believing it will change the clock mode and
without reading the binding doc first.

The description could then read something like

	micrel,rmii-reference-clock-select-inverted: RMII Reference
		Clock Select bit is inverted

	The RMII Reference Clock Select bit is inverted so that setting
	it selects 25 MHz rather than 50 MHz clock mode. 

	Note that this is only needed for PHY variants that has this bit
	inverted and that a clock reference ("rmii-ref" below) is always
	needed to select the actual mode.

> It's not very nice from Micrel to create Phys with exactly the same
> device id but the meaning of this bit reversed.

Not very nice at all.

Thanks,
Johan
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