Device tree population

[nomis]

Example template .dts: http://s85.org/6o9R3Ev2:view
Example compiled .dtb: http://s85.org/6A9h2c6X:raw

Could you automatically populate the following fields in the device tree file?

/memreserve/ (u32 offset, u32 size of VideoCore memory - this is not a normal attribute)
/memory/reg with the u32 memory range (e.g. 0x0 0x10000000 for 256MB)
/chosen/bootargs with the contents of the command line file (without any additional arguments)

/system/revision with the u32 system revision
/system/serial with the high u32 followed by the low u32 of the serial number

/axi/usb/hub/ethernet/mac-address with the system mac address (this is six u8 bytes in network byte order, e.g. 00:11:22:33:44:55)

/axi/dma/broadcom,channels with the u32 mask of allowed channels (this is currently on the command line as dma.dmachans)

/axi/sdhci/clock-frequency with the u32 clock frequency in Hz
/axi/uart0/clock-frequency with the u32 clock frequency in Hz

/display/broadcom,width with the u32 display pixel width (this is currently on the command line as bcm2708_fb.fbwidth)
/display/broadcom,height with the u32 display pixel height (this is currently on the command line as bcm2708_fb.fbheight)
/display/broadcom,depth with the u32 display bit depth (this is currently on the command line as bcm2708_fb.fbdepth)

If there's anything you think I've missed let me know (the setting for dwc_otg.lpm_enable=0 can be put in the static template so the GPU doesn't need to provide it).

[nomis]

Updated to use /system-serial instead of separate /system-serial-high and /system-serial-low (although I haven't changed the .dts/.dtb).

[nomis]

Updated to move the mac address to /axi/usb/hub/ethernet/mac-address.

I've been advised that putting a mac-address at / is going to be a problem we don't want to re-open. Putting it at this location exactly matches the physical hardware devices.

[popcornmix]

You did earlier say: "Everything's be32 so it should be simple to overwrite default values as required. There's already a placeholder for the memory"

But I think the bootargs breaks that. Looks like I have to decompile then compile the dtb file. Unless I've missed something?

[nomis]

I was sure I had seen padding in one of the .dts for this but I can't find one now, so you may need to do that. I'm not sure exactly how the format works but you might be able to append another string to the end.

[popcornmix]

What happens if you say:
chosen { bootargs = " "; };
(for a sufficiently large number of spaces)?

[nomis]

Problem solved!

Put this in arch/arm/mach-bcm2708/Makefile.boot:
DTC_FLAGS ?= -p 4096

[popcornmix]

Great. I'll start work on this issue.

[popcornmix]

Okay, I've had a go at filling in the required device tree fields. Let me know if there are any problems:
https://dl.dropbox.com/u/3669512/start.elf

[bootc]

Nearly. I haven't spent much time on this yet, but with disable_cmdline_tags=1 I get no command-line options in /chosen - or at least my kernel doesn't pick them up. With disable_cmdline_tags=0 it uses ATAGs I think, and the kernel doesn't boot because the device tree isn't there.

[popcornmix]

Can you try making space in the:
chosen { bootargs = " "; };
in bcm2835.dtsi. I will only fill in up to the original length of the bootargs string.

[bootc]

Oh it doesn't use the padding space left at the end of the dtb? I'll see if I can't give it a go in a few, but may not be able to until about 20:30.

[popcornmix]

From my limited understanding, the data in the bootargs is just contained inline with the devtree tags, so it's not possible to store that in the padding space without recompiling a new devtree.

It does seem to work if you store a string of, say, 1024 spaces in the bootargs, and I overwrite that with real command line (leaving length as 1024 and spaces intact).

I've updated the start.elf to not store the '\0' inside string, which I think is more correct (it makes is_printable_string return true).

P.S. I'm expecting you to define disable_cmdline_tags=1.

[bootc]

Trouble with the big empty string full of spaces is I doubt we'd ever be able to get a device tree with that into mainline. How does fdtput do it? Is http://git.jdl.com/gitweb/?p=dtc.git any help?

[popcornmix]

Looking at code, it won't
* TODO: add options to: * - expand fdt if value doesn't fit
and:
./fdtput -ts bcm2835.dtb /chosen bootargs "root=nfs" Error at 'bootargs': FDT_ERR_NOSPACE

If the big empty string is a blocker for upstreaming, then I'm sure we'll find a solution.
However it may be a temporary solution for the current developement.

[bootc]

Right, with the extra padding that lp0 has added when generating the .dtb (DTC_FLAGS ?= -p 4096) those should never trigger. The padding is added specifically so that fdtput can add in the command-line args without having to expand the fdt. Consider my code for building the .dtb files manually, below:

dtc -O dtb -o bcm2835-rpi-b.dtb -p 128 ~/Projects/linux-lp0/arch/arm/boot/dts/bcm2835-rpi-b.dts
fdtput -t x bcm2835-rpi-b.dtb /memory reg 0 0e000000
fdtput bcm2835-rpi-b.dtb / system-rev 2
fdtput -t x bcm2835-rpi-b.dtb / system-serial 0 12345678
fdtput -t hhx bcm2835-rpi-b.dtb / mac-address 11 22 33 44 55 66
fdtput bcm2835-rpi-b.dtb /display width 656
fdtput bcm2835-rpi-b.dtb /display height 416
fdtput bcm2835-rpi-b.dtb /display depth 16
fdtput -t x bcm2835-rpi-b.dtb /axi/dma channels 3c
fdtput -t s bcm2835-rpi-b.dtb /chosen bootargs "console=ttyAMA0,115200 debug earlyprintk root=/dev/mmcblk0p2 rootwait"

This works, including the bootargs bit at the bottom, because of the added 128 bytes of padding when I called dtc.