Re: [PATCH 4/4] ARM: zImage: allow supplementing appended DTB with traditional ATAG data

[David Brown <davidb@codeaurora.org>]

On Tue, Jun 21 2011, Shawn Guo wrote:

> On Tue, Jun 21, 2011 at 01:09:15AM -0400, Nicolas Pitre wrote:
>> From: Nicolas Pitre <nicolas.pitre@linaro.org>
>> 
>> Some old bootloaders can't be updated to a device tree capable one,
>> yet they provide ATAGs with memory configuration, the ramdisk address,
>> the kernel cmdline string, etc.  To allow a device tree enabled
>> kernel to be used with such bootloaders, it is necessary to convert those
>> ATAGs into FDT properties and fold them into the DTB appended to zImage.
>> 
>> Currently the following ATAGs are converted:
>> 
>> 	ATAG_CMDLINE
>> 	ATAG_MEM (up to 8 memory regions)
>> 	ATAG_INITRD2
>> 
>> If the corresponding information already exists in the appended DTB, it
>> is replaced, otherwise the required node is created to hold it.
>> 
>> The code looks for ATAGs at the location pointed by the value of r2 upon
>> entry into the zImage code.  If no ATAGs are found there, an attempt at
>> finding ATAGs at the typical 0x100 offset from start of RAM is made.
>> Otherwise the DTB is left unchanged.
>> 
>> Thisstarted from an older patch from John Bonesio <bones@secretlab.ca>,
>> with contributions from David Brown <davidb@codeaurora.org>.
>> 
>> Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
>> ---
>
> With this patch applied, I saw nothing coming from kernel on imx51
> babbage serial port.

Can you try seeing if it works with padding in the DTB that you are
using?  Right now, I'm using something like:

/ {
	...
	memory {
		reg = <0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0>;
	};
	chosen {
		bootargs = "                              "; /* Enough for arg */
		linux,initrd-start = <0>;
		linux,initrd-end = <0>;
	};
};

I get problems if the fdt code tries to expand the tree, even if I add
padding when running the dtc (I've tried -p 1024).

Hopefully, I'll get some time today to try and figure out what is going
on.

David

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