Subject: Re: [PATCH v10 5/5] [powerpc] Fix up fsl-flexcan device tree binding.

From: Robin Holt <[email-masked]>
Date: Wed, 10 Aug 2011 11:00:54 -0500

On Wed, Aug 10, 2011 at 02:36:20PM +0000, U Bhaskar-B22300 wrote:
> 
> 
> > -----Original Message-----
> > From: Robin Holt [mailto:[email-masked]]
> > Sent: Wednesday, August 10, 2011 7:46 PM
> > To: Wolfgang Grandegger
> > Cc: Robin Holt; Marc Kleine-Budde; U Bhaskar-B22300; Wood Scott-B07421;
> > [email-masked]; Kumar Gala; [email-masked]; PPC
> > list
> > Subject: Re: [PATCH v10 5/5] [powerpc] Fix up fsl-flexcan device tree
> > binding.
> > 
> > On Wed, Aug 10, 2011 at 03:47:43PM +0200, Wolfgang Grandegger wrote:
> > > Hi Robin,
> > >
> > > On 08/10/2011 05:06 AM, Robin Holt wrote:
> > > > In working with the socketcan developers, we have come to the
> > > > conclusion the Documentation...fsl-flexcan.txt device tree
> > > > documentation needs to be cleaned up.  The driver does not depend
> > > > upon any properties other
> > >
> > > Your first sentence could be misleading. Please just describe what the
> > > patch does and why, something like:
> > >
> > > "This patch cleans up the documentation of the device-tree binding for
> > > the Flexcan devices on Freescale's PowerPC and ARM cores. Extra
> > > properties are not needed as the frequency of the source clock is
> > > fixed..." and so on.
> > 
> > I borrowed heavily from your message. ;)
> > 
> > > > than the required properties so we are removing the file.
> > > > Additionally, the p1010*dts* files are not following the standard
> > > > for node naming in that they have a trailing -v1.0.
> > >
> > > > Signed-off-by: Robin Holt <[email-masked]>
> > > > To: Marc Kleine-Budde <[email-masked]>,
> > > > To: Wolfgang Grandegger <[email-masked]>,
> > > > To: U Bhaskar-B22300 <[email-masked]>
> > > > To: Scott Wood <[email-masked]>
> > > > Cc: [email-masked],
> > > > Cc: [email-masked],
> > > > Cc: PPC list <[email-masked]>
> > > > Cc: Kumar Gala <[email-masked]>
> > > > ---
> > > >  .../devicetree/bindings/net/can/fsl-flexcan.txt    |   61 ----------
> > ----------
> > > >  arch/powerpc/boot/dts/p1010rdb.dts                 |    8 ---
> > > >  arch/powerpc/boot/dts/p1010si.dtsi                 |    8 +-
> > > >  3 files changed, 4 insertions(+), 73 deletions(-)  delete mode
> > > > 100644 Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > > >
> > > > diff --git
> > > > a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > > > b/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > > > deleted file mode 100644
> > > > index 1a729f0..0000000
> > > > --- a/Documentation/devicetree/bindings/net/can/fsl-flexcan.txt
> > > > +++ /dev/null
> > > > @@ -1,61 +0,0 @@
> > > > -CAN Device Tree Bindings
> > > > -------------------------
> > > > -2011 Freescale Semiconductor, Inc.
> > > > -
> > > > -fsl,flexcan-v1.0 nodes
> > > > ------------------------
> > > > -In addition to the required compatible-, reg- and
> > > > interrupt-properties, you can -also specify which clock source shall
> > be used for the controller.
> > > > -
> > > > -CPI Clock- Can Protocol Interface Clock
> > > > -	This CLK_SRC bit of CTRL(control register) selects the clock source
> > to
> > > > -	the CAN Protocol Interface(CPI) to be either the peripheral clock
> > > > -	(driven by the PLL) or the crystal oscillator clock. The selected
> > clock
> > > > -	is the one fed to the prescaler to generate the Serial Clock
> > (Sclock).
> > > > -	The PRESDIV field of CTRL(control register) controls a prescaler
> > that
> > > > -	generates the Serial Clock (Sclock), whose period defines the
> > > > -	time quantum used to compose the CAN waveform.
> > > > -
> > > > -Can Engine Clock Source
> > > > -	There are two sources for CAN clock
> > > > -	- Platform Clock  It represents the bus clock
> > > > -	- Oscillator Clock
> > > > -
> > > > -	Peripheral Clock (PLL)
> > > > -	--------------
> > > > -		     |
> > > > -		    ---------		      -------------
> > > > -		    |       |CPI Clock	      | Prescaler |       Sclock
> > > > -		    |       |---------------->| (1.. 256) |------------>
> > > > -		    ---------		      -------------
> > > > -                     |  |
> > > > -	--------------  ---------------------CLK_SRC
> > > > -	Oscillator Clock
> > > > -
> > > > -- fsl,flexcan-clock-source : CAN Engine Clock Source.This property
> > selects
> > > > -			     the peripheral clock. PLL clock is fed to the
> > > > -			     prescaler to generate the Serial Clock (Sclock).
> > > > -			     Valid values are "oscillator" and "platform"
> > > > -			     "oscillator": CAN engine clock source is
> > oscillator clock.
> > > > -			     "platform" The CAN engine clock source is the bus
> > clock
> > > > -		             (platform clock).
> > > > -
> > > > -- fsl,flexcan-clock-divider : for the reference and system clock, an
> > additional
> > > > -			      clock divider can be specified.
> > > > -- clock-frequency: frequency required to calculate the bitrate for
> > FlexCAN.
> > > > -
> > > > -Note:
> > > > -	- v1.0 of flexcan-v1.0 represent the IP block version for P1010
> > SOC.
> > > > -	- P1010 does not have oscillator as the Clock Source.So the default
> > > > -	  Clock Source is platform clock.
> > > > -Examples:
> > > > -
> > > > -	can0@1c000 {
> > > > -		compatible = "fsl,flexcan-v1.0";
> > > > -		reg = <0x1c000 0x1000>;
> > > > -		interrupts = <48 0x2>;
> > > > -		interrupt-parent = <&mpic>;
> > > > -		fsl,flexcan-clock-source = "platform";
> > > > -		fsl,flexcan-clock-divqider = <2>;
> > > > -		clock-frequency = <fixed by u-boot>;
> > > > -	};
> > >
> > > Do we really want to drop the documentation for that binding. I think
> > > something like the following text would be still useful:
> > >
> > > ------------------------
> > > Flexcan CAN contoller on Freescale's ARM and PowerPC processors
> > >
> > > Required properties:
> > >
> > > - compatible : Should be "fsl,flexcan" and optionally
> > >                "fsl,flexcan-<processor>"
> > > - reg : Offset and length of the register set for this device
> > > - interrupts : Interrupt tuple for this device
> > >
> > > Example:
> > >
> > >   can@1c000 {
> > >           compatible = "fsl,p1010-flexcan", "fsl,flexcan";
> > >           reg = <0x1c000 0x1000>;
> > >           interrupts = <48 0x2>;
> > >           interrupt-parent = <&mpic>;
> > >   };
> > > -------------------------
> > 
> > Done, except the
> > >           compatible = "fsl,p1010-flexcan", "fsl,flexcan";
> > 
> > line is
> > 	compatible = "fsl,flexcan", "fsl,flexcan-p1010";
> > 
> > >
> > > What do you think?
> > >
> > > > diff --git a/arch/powerpc/boot/dts/p1010rdb.dts
> > > > b/arch/powerpc/boot/dts/p1010rdb.dts
> > > > index 6b33b73..d6a0bb2 100644
> > > > --- a/arch/powerpc/boot/dts/p1010rdb.dts
> > > > +++ b/arch/powerpc/boot/dts/p1010rdb.dts
> > > > @@ -169,14 +169,6 @@
> > > >  			};
> > > >  		};
> > > >
> > > > -		can0@1c000 {
> > > > -			fsl,flexcan-clock-source = "platform";
> > > > -		};
> > > > -
> > > > -		can1@1d000 {
> > > > -			fsl,flexcan-clock-source = "platform";
> > > > -		};
> > > > -
> > > >  		usb@22000 {
> > > >  			phy_type = "utmi";
> > > >  		};
> > > > diff --git a/arch/powerpc/boot/dts/p1010si.dtsi
> > > > b/arch/powerpc/boot/dts/p1010si.dtsi
> > > > index 7f51104..20c396d 100644
> > > > --- a/arch/powerpc/boot/dts/p1010si.dtsi
> > > > +++ b/arch/powerpc/boot/dts/p1010si.dtsi
> > > > @@ -141,19 +141,19 @@
> > > >  		};
> > > >
> > > >  		can0@1c000 {
> > > > -			compatible = "fsl,flexcan-v1.0";
> > > > +			compatible = "fsl,p1010-flexcan",
> > > > +					"fsl,flexcan";
> > >
> > > Does fit on one line.
> > >
> > > >  			reg = <0x1c000 0x1000>;
> > > >  			interrupts = <48 0x2>;
> > > >  			interrupt-parent = <&mpic>;
> > > > -			fsl,flexcan-clock-divider = <2>;
> > > >  		};
> > > >
> > > >  		can1@1d000 {
> > > > -			compatible = "fsl,flexcan-v1.0";
> > > > +			compatible = "fsl,p1010-flexcan",
> > > > +					"fsl,flexcan";
> > >
> > > Ditto
> > >
> > > >  			reg = <0x1d000 0x1000>;
> > > >  			interrupts = <61 0x2>;
> > > >  			interrupt-parent = <&mpic>;
> > > > -			fsl,flexcan-clock-divider = <2>;
> > > >  		};
> > > >
> > > >  		L2: l2-cache-controller@20000 {
> > >
> > > Please also correct the node names (not using the number suffix).
> > 
> > So the node names should be
> > 		can@1c000 {
> > 		can@1d000 {
> > correct?
> > 
> [Bhaskar] As there are two CAN controllers on P1010,So won't it be better
> 	    to distinguish it by can0 and can1 instead by simple "can" ?

It looks like the way to do that is to assign a label to those devices
and then associate the label with an alias.  I have no idea how that
works under the hood, but it is the way other files are set up.  Take a
look at arch/powerpc/boot/dts/bamboo.dts for how they define the serial
interfaces.

Grant or Wolfgang, is that the right way to handle the concern about
names or does it have no practical effect with the Linux kernel?

Thanks,
Robin