[RFC 5/5] [powerpc] Implement a p1010rdb clock source.

[U Bhaskar-B22300]

> -----Original Message-----
> From: Wolfgang Grandegger [mailto:wg at grandegger.com]
> Sent: Tuesday, August 09, 2011 4:19 PM
> To: U Bhaskar-B22300
> Cc: Marc Kleine-Budde; socketcan-core at lists.berlios.de;
> netdev at vger.kernel.org; Devicetree-discuss at lists.ozlabs.org
> Subject: Re: [RFC 5/5] [powerpc] Implement a p1010rdb clock source.
> 
> On 08/09/2011 11:27 AM, U Bhaskar-B22300 wrote:
> >
> >
> >> -----Original Message-----
> >> From: Wolfgang Grandegger [mailto:wg at grandegger.com]
> >> Sent: Tuesday, August 09, 2011 2:03 PM
> >> To: U Bhaskar-B22300
> >> Cc: Marc Kleine-Budde; socketcan-core at lists.berlios.de;
> >> netdev at vger.kernel.org; Devicetree-discuss at lists.ozlabs.org
> >> Subject: Re: [RFC 5/5] [powerpc] Implement a p1010rdb clock source.
> >>
> >> Hi Bhaskar,
> >>
> >> On 08/09/2011 09:57 AM, U Bhaskar-B22300 wrote:
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: Marc Kleine-Budde [mailto:mkl at pengutronix.de]
> >>>> Sent: Tuesday, August 09, 2011 12:23 AM
> >>>> To: Wolfgang Grandegger
> >>>> Cc: socketcan-core at lists.berlios.de; netdev at vger.kernel.org; U
> >>>> Bhaskar- B22300
> >>>> Subject: Re: [RFC 5/5] [powerpc] Implement a p1010rdb clock source.
> >>>>
> >>>> On 08/08/2011 05:33 PM, Wolfgang Grandegger wrote:
> >>>>>> ACK - The device tree bindings as in mainline's Documentation is
> >>>>>> a
> >>>> mess.
> >>>>>> If the powerpc guys are happy with a clock interfaces based
> >>>>>> approach somewhere in arch/ppc, I'm more than happy to remove:
> >>>>>> - fsl,flexcan-clock-source (not implemented, even in the fsl
> >>>>>> driver)
> >>> [Bhaskar]I have pushed the FlexCAN series of patches, It contains
> >>> the usage of all the fields posted in the FlexCAN bindings at
> >>> http://git.kernel.org/?p=linux/kernel/git/stable/linux-3.0.y.git;a=b
> >>> lo
> >>> b;f=Documentation/devicetree/bindings/net/can/fsl-flexcan.txt;h=1a72
> >>> 9f
> >>> 089866259ef82d0db5893ff7a8c54d5ccf;hb=94ed5b4788a7cdbe68bc7cb8516972
> >>> cb
> >>> ebdc8274
> >>
> >> As Marc already pointed out, Robin already has a much more advanced
> >> patch stack in preparation. Especially your patches do not care about
> >> the already existing Flexcan core on the Freescale's ARM socks.
> > [Bhaskar] No, the patches are taking care of the existing ARM
> functionality.
> > 	I have not tested on the ARM based board, but the patches are made
> in a
> >       Manner that it should not break the ARM based functionality.
> >>
> >>>>>>
> >>>>>> - fsl,flexcan-clock-divider \__ replace with code in arch/ppc, or
> >>>>>> - clock-frequency           /   a single clock-frequency attribute
> >>>>>
> >>>>> In the "net-next-2.6" tree there is also:
> >>>>>
> >>>>>  $ grep flexcan arch/powerpc/boots/dts/*.dts
> >>>>>   p1010rdb.dts:			fsl,flexcan-clock-source =
> >> "platform";
> >>>>>   p1010rdb.dts:			fsl,flexcan-clock-source =
> >> "platform";
> >>>>>   p1010si.dtsi:			compatible = "fsl,flexcan-v1.0";
> >>>>>   p1010si.dtsi:			fsl,flexcan-clock-divider = <2>;
> >>>>>   p1010si.dtsi:			compatible = "fsl,flexcan-v1.0";
> >>>>>   p1010si.dtsi:			fsl,flexcan-clock-divider = <2>;
> >>>>>
> >>>>> Especially the fsl,flexcan-clock-divider = <2>; might make people
> >>>>> think, that they could set something else.
> >>>>
> >>> [Bhaskar] As it is mentioned in the Flexcan bindings, the need of
> >> fsl,flexcan-clock-divider = <2>;
> >>> 	    But I kept it as "2" because FlexCan clock source is the
> >> platform clock and it is CCB/2
> >>> 	    If the "2" is misleading, the bindings can be changed or some
> >> text can be written to make the meaning of "2"
> >>>           Understandable , Please suggest ..
> >>
> >> The clock source and frequency is fixed. Why do we need an extra
> >> properties for that. We have panned to remove these bogus bindings
> >> from the Linux kernel, which sneaked in *without* any review on the
> >> relevant mailing lists (at least I have not realized any posting). We
> >> do not think they are really needed. They just confuse the user. We
> >> also prefer to use the compatibility string "fsl,flexcan" instead
> >> "fsl,flexcan-v1.0". It's unusual to add a version number, which is
> >> for the Flexcan on the PowerPC cores only, I assume, but there will
> >> be device tree for ARM soon. A proper compatibility string would be
> >> "fsl,p1010-flexcan" if we really need to distinguish.
> >>
> > [Bhaskar] About clock source.. There can be two sources of clock for
> the CAN.
> > 	Oscillator or the platform clock, but at present only platform
> clock is supported
> > 	in P1010.If we remove the fsl,flexcan-clock-source property, we
> will lost the flexibility
> > 	of changing the clock source ..
> >
> >           About clock-frequency... it is also not fixed. It depends on
> the platform clock which in turns
> >           Depends on the CCB clock. So it will be better to keep clock-
> frequency property which is getting fixed via u-boot.
> 
> The frequency is fixed to CCB-frequency / 2. Will that ever change? What
> can we expect from future Flexcan hardware? Will it support further clock
> sources?
[Bhaskar] Yes the frequency will always be CCB-frequency/2.Even if the CCB gets changed that will be taken care by the u-boot fixup code for
	clock-frequency. clock-frequency is not filled by somebody in the dts file. It will be done by u-boot.
	For clock source,I can't say right now, that's why I have kept a property for this in the can node. So that in future, we need to fill it 
	appropriately
> 
> Wolfgang.