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

From: Robin Holt <[email-masked]>
Date: Wed, 10 Aug 2011 12:20:40 -0500

On Wed, Aug 10, 2011 at 12:17:45PM -0500, Kumar Gala wrote:
> 
> On Aug 10, 2011, at 12:16 PM, Robin Holt wrote:
> 
> > On Wed, Aug 10, 2011 at 11:53:15AM -0500, Kumar Gala wrote:
> >> 
> >> On Aug 10, 2011, at 11:00 AM, Robin Holt wrote:
> >> 
> >>> 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?
> >> 
> >> It has not effect.  The label is just if you need to reference it via some other means.
> > 
> > Does the alias have an effect?
> 
> nope

Then how does the device number get associated with a particular device
and how is user-space ensured a consistent namespace?

Robin