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

On Wed, Aug 10, 2011 at 12:17:45PM -0500, Kumar Gala wrote:

On Aug 10, 2011, at 12:16 PM, Robin Holt wrote:

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On Wed, Aug 10, 2011 at 11:53:15AM -0500, Kumar Gala wrote:

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On Aug 10, 2011, at 11:00 AM, Robin Holt wrote:

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On Wed, Aug 10, 2011 at 02:36:20PM +0000, U Bhaskar-B22300 wrote:

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-----Original Message-----
From: Robin Holt [mailto:holt-sJ/iWh9BUns@public.gmane.org]
Sent: Wednesday, August 10, 2011 7:46 PM
To: Wolfgang Grandegger
Cc: Robin Holt; Marc Kleine-Budde; U Bhaskar-B22300; Wood Scott-B07421;
netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Kumar Gala; socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org; 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:

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Hi Robin,

On 08/10/2011 05:06 AM, Robin Holt wrote:

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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. ;)

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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.

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Signed-off-by: Robin Holt <holt-sJ/iWh9BUns@public.gmane.org>
To: Marc Kleine-Budde <redacted>,
To: Wolfgang Grandegger <redacted>,
To: U Bhaskar-B22300 <redacted>
To: Scott Wood <redacted>
Cc: socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org,
Cc: netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Cc: PPC list <linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>
Cc: Kumar Gala <redacted>
---
.../devicetree/bindings/net/can/fsl-flexcan.txt    |   61 ----------

----------

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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.

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-
-CPI Clock- Can Protocol Interface Clock
-	This CLK_SRC bit of CTRL(control register) selects the clock source

to

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-	the CAN Protocol Interface(CPI) to be either the peripheral clock
-	(driven by the PLL) or the crystal oscillator clock. The selected

clock

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-	is the one fed to the prescaler to generate the Serial Clock

(Sclock).

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-	The PRESDIV field of CTRL(control register) controls a prescaler

that

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-	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

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-			     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.

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-			     "platform" The CAN engine clock source is the bus

clock

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-		             (platform clock).
-
-- fsl,flexcan-clock-divider : for the reference and system clock, an

additional

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-			      clock divider can be specified.
-- clock-frequency: frequency required to calculate the bitrate for

FlexCAN.

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-
-Note:
-	- v1.0 of flexcan-v1.0 represent the IP block version for P1010

SOC.

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-	- 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

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        compatible = "fsl,p1010-flexcan", "fsl,flexcan";

line is
	compatible = "fsl,flexcan", "fsl,flexcan-p1010";

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What do you think?

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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.

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			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

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			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