On Mon, Feb 21, 2011 at 2:46 AM, Shawn Guo [off-list ref] wrote:

Here is what I copied from booting-without-of.txt.

=====
 f) the /soc<SOCname> node

 This node is used to represent a system-on-a-chip (SoC) and must be
 present if the processor is a SoC. The top-level soc node contains
 information that is global to all devices on the SoC. The node name
 should contain a unit address for the SoC, which is the base address
 of the memory-mapped register set for the SoC. The name of an SoC
 node should start with "soc", and the remainder of the name should
 represent the part number for the soc.  For example, the MPC8540's
 soc node would be called "soc8540".

 Required properties:

   - ranges : Should be defined as specified in 1) to describe the
     translation of SoC addresses for memory mapped SoC registers.
   - bus-frequency: Contains the bus frequency for the SoC node.
     Typically, the value of this field is filled in by the boot
     loader.
   - compatible : Exact model of the SoC


 Recommended properties:

   - reg : This property defines the address and size of the
     memory-mapped registers that are used for the SOC node itself.
     It does not include the child device registers - these will be
     defined inside each child node.  The address specified in the
     "reg" property should match the unit address of the SOC node.
   - #address-cells : Address representation for "soc" devices.  The
     format of this field may vary depending on whether or not the
     device registers are memory mapped.  For memory mapped
     registers, this field represents the number of cells needed to
     represent the address of the registers.  For SOCs that do not
     use MMIO, a special address format should be defined that
     contains enough cells to represent the required information.
     See 1) above for more details on defining #address-cells.
   - #size-cells : Size representation for "soc" devices
   - #interrupt-cells : Defines the width of cells used to represent
      interrupts.  Typically this value is <2>, which includes a
      32-bit number that represents the interrupt number, and a
      32-bit number that represents the interrupt sense and level.
      This field is only needed if the SOC contains an interrupt
      controller.

 The SOC node may contain child nodes for each SOC device that the
 platform uses.  Nodes should not be created for devices which exist
 on the SOC but are not used by a particular platform. See chapter VI
 for more information on how to specify devices that are part of a SOC.

 Example SOC node for the MPC8540:

       soc8540@e0000000 {
               #address-cells = <1>;
               #size-cells = <1>;
               #interrupt-cells = <2>;
               device_type = "soc";
               ranges = <00000000 e0000000 00100000>
               reg = <e0000000 00003000>;
               bus-frequency = <0>;
       }
=====

I'm seeing the babbage.dts defined "soc" so differently than the
document requires.

quoted

+       soc {
+               #address-cells = <0x1>;
+               #size-cells = <0x1>;
+               device_type = "soc";
+               compatible = "simple-bus";
+               ranges = <0x0 0x0 0xffffffff>;
+
+               tzic {
+                       #address-cells = <0x0>;
+                       #interrupt-cells = <0x1>;
+                       interrupt-controller;
+                       reg = <0xe0000000 0x1000>;
+                       compatible = "fsl,tzic";
+                       device_type = "tzic";
+                       phandle = <0x1>;
+               };
+       };

The document is a little out of date in that it doesn't reflect all of
the current best practices.  It does need to be updated, but I'll
respond to the specific questions here...

* The soc node name has neither part number nor base address

Part number isn't necessary because the 'compatible' property is
supposed to be used to identify the exact device.  Base address must
be part of any node that has a 'reg' property.  In this particular
example, neither is the case so it is okay.

* Even required property "bus-frequency" is missing

bus-frequency isn't required.

* The document "Appendix A - Sample SOC node for MPC8540" defines
every device node under "soc", while babbage.dts has most devices
outside the "soc" node.

The 'soc' node thing was something we started when new PowerPC SoC
machines were created.  However, it doesn't necessarily reflect the
best practice.  Ideally, the dt structure will match the physical
structure of the chip.  So, if a chip has multiple internal busses,
then the dts should probably have a node for each bus, and then each
device a child of the bus node.  However, having a single containing
'soc' node for all on-chip busses and devices is probably a good thing
to preserve.

Are what the document describes requirements we must follow or just
suggestions we can take or not?

Crafting a .dts file and device tree bindings are as much an art as a
science.  There are some things that aren't hard rules, but there are
reasons behind why most are done in a certain way.  The best way to
develop a new .dts file is to draft up your best effort, post it for
review, and listen to the comments that come back.  :-)

Besides the overall question above, some nitpicking embedded below ...

On 18 February 2011 16:12, Jason Liu [off-list ref] wrote:

quoted

Signed-off-by: Jason Liu <redacted>
---
 arch/arm/boot/dts/babbage.dts |  117 +++++++++++++++++++++++++++++++++++++++++
 1 files changed, 117 insertions(+), 0 deletions(-)

diff --git a/arch/arm/boot/dts/babbage.dts b/arch/arm/boot/dts/babbage.dts
new file mode 100644
index 0000000..7ee26f1
--- /dev/null
+++ b/arch/arm/boot/dts/babbage.dts

@@ -0,0 +1,117 @@
+/dts-v1/;
+
+/ {
+       model = "mx51_babbage";

This is a human readable string.  You can write something like
"Freescale i.MX51 Babbage" here.

quoted

+       compatible = "fsl,mx51_babbage";

Use dash '-' instead of underscores '_' in compatible values.

quoted

+       #address-cells = <0x1>;
+       #size-cells = <0x1>;
+       #interrupt-cells = <0x1>;
+       interrupt-parent = <0x1>;
+
+       memory {
+               device_type = "memory";
+               reg = <0x90000000 0x20000000>;
+       };
+
+       chosen {
+               bootargs = "console=ttymxc1,115200n8 debug earlyprintk";
+       };
+
+       soc {
+               #address-cells = <0x1>;
+               #size-cells = <0x1>;
+               device_type = "soc";

Drop the "device_type" property.  It only makes sense for machines
with real Open Firmware.

quoted

+               compatible = "simple-bus";

Need to specify the specific chip here:

        compatible = "fsl,imx51-soc", "simple-bus";

quoted

+               ranges = <0x0 0x0 0xffffffff>;

one-to-one mapping of the full address range can be specified simply
with an empty ranges property:

        ranges;

quoted

+
+               tzic {

tzic@e0000000 {

quoted

+                       #address-cells = <0x0>;
+                       #interrupt-cells = <0x1>;
+                       interrupt-controller;
+                       reg = <0xe0000000 0x1000>;
+                       compatible = "fsl,tzic";

Specify the exact chip in the compatible property:

compatible = "fsl,imx51-tzic";

quoted

+                       device_type = "tzic";

Drop device type

quoted

+                       phandle = <0x1>;

Drop phandle; dtc adds phandles automatically.

quoted

+               };
+       };
+
+       clocks {
+               #address-cells = <1>;
+               #size-cells = <0>;
+

Can we use hex value here to keep the consistency throughout the file?

For #address-cells and #size-cells use decimal integers.

quoted

+               uart_clk0: uart@0 {

@0 should only be specified if the node has a 'reg = <0>' property.
In this case it doesn't so either 'reg' should be added, or '@0'
should be removed.

quoted

+                       compatible = "clock";
+                       clock-outputs = "imx-uart.0";
+               };
+
+               uart_clk1: uart@1{

Can we put a space before "{" to keep the consistency throughout the file?

Yes, please.

quoted

+                       compatible = "clock";
+                       clock-outputs = "imx-uart.1";
+               };
+
+               uart_clk2: uart@2{

ditto

quoted

+                       compatible = "clock";
+                       clock-outputs = "imx-uart.2";
+               };
+
+               fec_clk: @0{

"@0" is not a valid node name.

ditto

quoted

+                       compatible = "clock";
+                       clock-outputs = "fec.0";
+               };
+       };
+
+       spba@70000000 {
+               #address-cells = <0x1>;
+               #size-cells = <0x1>;
+               device_type = "soc";

Drop device type.

quoted

+               compatible = "simple-bus";

Specify the actual device here before "simple-bus"

quoted

+               ranges = <0x0 0x70000000 0x100000>;
+
+               imx-uart@C000 {

Use lowercase for all address/offset to keep consistency throughout the file?

yes.

quoted

+                       compatible = "imx-uart";
+                       reg = <0xc000 0x1000>;
+                       interrupts = <0x21>;
+                       rts-cts;
+                       uart-clock = < &uart_clk2 >, "uart";

Remove the space after "<" and before ">" to keep consistency
throughout the file?

quoted

+               };
+       };
+
+       aips@73f00000 {
+               #address-cells = <0x1>;
+               #size-cells = <0x1>;
+               device_type = "soc";
+               compatible = "simple-bus";
+               ranges = <0x0 0x73f00000 0x100000>;
+
+               imx-uart@BC000 {

ditto

quoted

+                       compatible = "imx-uart";
+                       reg = <0xbc000 0x1000>;
+                       interrupts = <0x1f>;
+                       rts-cts;
+                       uart-clock = < &uart_clk0 >, "uart";

Remove the space after "<" and before ">"?

quoted

+               };
+
+               imx-uart@C0000 {

Lowercase for offset?

quoted

+                       compatible = "imx-uart";
+                       reg = <0xc0000 0x1000>;
+                       interrupts = <0x20>;
+                       rts-cts;
+                       uart-clock = <&uart_clk1>, "uart";
+               };
+       };
+
+       aips@83f00000 {
+               #address-cells = <0x1>;
+               #size-cells = <0x1>;
+               device_type = "soc";
+               compatible = "simple-bus";
+               ranges = <0x0 0x83f00000 0x100000>;
+
+               fec@EC000 {

ditto

quoted

+                       compatible = "fec";
+                       reg = <0xec000 0x1000>;
+                       interrupts = <0x57>;
+                       fec_clk-clock = < &fec_clk >, "fec";
+               };
+       };
+};
--
1.7.0.4

--
Regards,
Shawn

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