Message-ID: <1372425670.21065.61.camel@cumari.coelho.fi>
Date:	Fri, 28 Jun 2013 16:21:10 +0300
From:	Luciano Coelho <coelho@...com>
To:	<mturquette@...aro.org>
CC:	<balbi@...com>, Mark Rutland <mark.rutland@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"linux-arm@...r.kernel.org" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] Documentation: dt: bindings: TI WiLink modules

On Fri, 2013-06-28 at 15:18 +0300, Felipe Balbi wrote:
> On Fri, Jun 28, 2013 at 03:13:52PM +0300, Luciano Coelho wrote:
> > On Fri, 2013-06-28 at 14:41 +0300, Felipe Balbi wrote:
> > > On Fri, Jun 28, 2013 at 02:22:11PM +0300, Luciano Coelho wrote:
> > > > On Fri, 2013-06-28 at 13:31 +0300, Luciano Coelho wrote:
> > > > > (fixed Mike's address)
> > > > > 
> > > > > On Fri, 2013-06-28 at 11:21 +0100, Mark Rutland wrote:
> > > > > > On Fri, Jun 28, 2013 at 10:53:35AM +0100, Luciano Coelho wrote:
> > > > > > > On Fri, 2013-06-28 at 10:38 +0100, Mark Rutland wrote:
> > > > > > > > On Tue, Jun 25, 2013 at 09:35:30AM +0100, Luciano Coelho wrote:
> > > > > > > > > +Optional properties:
> > > > > > > > > +--------------------
> > > > > > > > > +
> > > > > > > > > +- refclock: the internal WLAN reference clock frequency (required for
> > > > > > > > > +  WiLink6 and WiLink7; not used for WiLink8).  Must be one of the
> > > > > > > > > +  following:
> > > > > > > > > +	0 = 19.2 MHz
> > > > > > > > > +	1 = 26.0 MHz
> > > > > > > > > +	2 = 38.4 MHz
> > > > > > > > > +	3 = 52.0 MHz
> > > > > > > > > +	4 = 38.4 MHz, XTAL
> > > > > > > > > +	5 = 26.0 MHz, XTAL
> > > > > > > > > +
> > > > > > > > > +- tcxoclock: the internal WLAN TCXO clock frequency (required for
> > > > > > > > > +  WiLink7 not used for WiLink6 and WiLink8).  Must be one of the
> > > > > > > > > +  following:
> > > > > > > > > +	0 = 19.200 MHz
> > > > > > > > > +	1 = 26.000 MHz
> > > > > > > > > +	2 = 38.400 MHz
> > > > > > > > > +	3 = 52.000 MHz
> > > > > > > > > +	4 = 16.368 MHz
> > > > > > > > > +	5 = 32.736 MHz
> > > > > > > > > +	6 = 16.800 MHz
> > > > > > > > > +	7 = 33.600 MHz
> > > > > > > > 
> > > > > > > > This looks suspiciously like what we have the common clock bindings for:
> > > > > > > > 
> > > > > > > > refclk {
> > > > > > > > 	compatible = "fixed-clock";
> > > > > > > > 	#clock-cells = <0>;
> > > > > > > > 	clock-frequency = <19200000>;
> > > > > > > > }
> > > > > > > > 
> > > > > > > > wilink {
> > > > > > > > 	compatible = "ti,wilink7";
> > > > > > > > 	interrupt-parent = <&some_interrupt_controller>;
> > > > > > > > 	interrupts = <0 1 1>;
> > > > > > > > 	clocks = <&refclk>, <&refclk>;
> > > > > > > > 	clock-names = "refclk", "txoclk";
> > > > > > > > };
> > > > > > > > 
> > > > > > > > Could you not use them?
> > > > > > > 
> > > > > > > Hmmm... this actually does look good.  But these are internal clocks in
> > > > > > > the modules, they cannot be accessed from outside.  Does it make sense
> > > > > > > to register them with the clock framework?
> > > > > > 
> > > > > > Given we already have a common way of describing clocks, I think it
> > > > > > makes sense to use it -- people already understand the common bindings,
> > > > > > and it's less code to add add to the kernel. I don't think the fact
> > > > > > these clocks are internal should prevent us from describing them as we
> > > > > > would an external clock.
> > > > > 
> > > > > Yes, I agree with you.  Thanks for the suggestion! I think it will look
> > > > > much better.  And now that I dug a bit more into the code, I can see
> > > > > that there are only structs being populated, so there shouldn't be any
> > > > > other side-effects.
> > > > 
> > > > Hmmm, one thing that escaped me.  Besides the frequency, I also need a
> > > > boolean that tells if the clock is XTAL or not.  I can't figure out how
> > > > to pass this if I use the generic clock framework.  Any suggestions?
> > > 
> > > Could you use clock-output-names for that ?
> > > 
> > > XTAL clock:
> > > 
> > > refclk {
> > > 	compatible = "fixed-clock";
> > > 	#clock cells = <0>;
> > > 	clock-frequency = <19200000>;
> > > 	clock-output-names = "xtal";
> > > };
> > > 
> > > non-XTAL clock:
> > > 
> > > refclk {
> > > 	compatible = "fixed-clock";
> > > 	#clock cells = <0>;
> > > 	clock-frequency = <19200000>;
> > > 	clock-output-names = "osc"; /* any better name ? */
> > > };
> > 
> > This starts looking a bit hacky.  Using the output name as a flag is not
> > very pretty.
> > 
> > I think it would be better to have a separate flag for it in the wlan
> > node.  Like an optional "refclock-xtal" boolean or something.  The
> > downside of this is that we would be adding information about the clock
> > details in the wilink node. :(
> > 
> > OTOH, we could add a flag to the generic clock binding? A new optional
> > boolean that tells whether the clock is XTAL or not:
> > 
> > refclk {
> > 	compatible = "fixed-clock";
> > 	#clock cells = <0>;
> > 	clock-frequency = <19200000>;
> > 	clock-xtal;
> > };
> > 
> > Do you think that would make sense?
> 
> sure, that looks alright to me. Surely there are other devices out there
> who want to know if the clock comes from a crystal or not ?!?

Mike, what do you think about this idea? If it sounds okay to you, I can
cook up a patch adding this flag.

--
Cheers,
Luca.

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