Re: [PATCH 0/3] patches to allow DTB to be appended to the ARM zImage

[Rob Herring <robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 06/14/2011 06:50 PM, Nicolas Pitre wrote:
> On Tue, 14 Jun 2011, Rob Herring wrote:
> 
>> On 06/14/2011 03:32 PM, Arnd Bergmann wrote:
>>> On Tuesday 14 June 2011 19:28:49 Nicolas Pitre wrote:
>>>> On Tue, 14 Jun 2011, Tony Lindgren wrote:
>>>>
>>>>> * Nicolas Pitre <nicolas.pitre-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> [110614 00:04]:
>>>>>> +
>>>>>> +   for_each_tag(atag, atag_list) {
>>>>>> +           if (atag->hdr.tag == ATAG_CMDLINE) {
>>>>>> +                   setprop_string(dt, "/chosen", "bootargs",
>>>>>> +                                     atag->u.cmdline.cmdline);
>>>>>> +           } else if (atag->hdr.tag == ATAG_MEM) {
>>>>>> +                   uint32_t mem_reg_property[2];
>>>>>> +                   mem_reg_property[0] = cpu_to_fdt32(atag->u.mem.start);
>>>>>> +                   mem_reg_property[1] = cpu_to_fdt32(atag->u.mem.size);
>>>>>> +                   setprop(dt, "/memory", "reg", mem_reg_property,
>>>>>> +                              sizeof(mem_reg_property));
>>>>>> +           } else if (atag->hdr.tag == ATAG_INITRD2) {
>>>>>> +                   uint32_t initrd_start, initrd_size;
>>>>>> +                   initrd_start = atag->u.initrd.start;
>>>>>> +                   initrd_size = atag->u.initrd.size;
>>>>>> +                   setprop_cell(dt, "/chosen", "linux,initrd-start",
>>>>>> +                                   initrd_start);
>>>>>> +                   setprop_cell(dt, "/chosen", "linux,initrd-end",
>>>>>> +                                   initrd_start + initrd_size);
>>>>>> +           }
>>>>>> +   }
>>>>>
>>>>> I think Russell posted a complete list of the ATAGs to translate
>>>>> somewhere, but at least ATAG_REVISION is missing here. That's being
>>>>> used quite a bit as system_rev to set things dynamically.
>>>>
>>>> No problem.  This is a work in progress.  We still can test the concept 
>>>> and fine tune the actual set of ATAGs being translated.
>>>
>>> Let's talk about the revision field now, because it doesn't have a
>>> direct correspondence in existing attributes.
>>>
>>> Functionality-wise, this would probably be the "compatible" property
>>> of the root node, with its most specific name to match, but that's not
>>> trivial to generate.
>>>
>>> In some cases, the system revisions have significant differences in their
>>> devices (why else would you care about the revision), which means that you
>>> actually need a different device tree per revision anyway. If that's the
>>> common case, we could just ignore it completely or instead have a way
>>> to choose a specific device tree from a list based on the revision.
>>>
>>> Another option would be to merge both the ATAG_REVISION and ATAG_SERIAL
>>> into a string and put them into the root "serial-number" property that
>>> is fairly easy to do, but would be harder to parse if you actually rely
>>> on specific values.
>>>
>>
>> IIRC, system_rev at least can be specified on the kernel command line,
>> so you could just append the cmd line. However, if you force the
>> built-in command line to be used that would not work,
> 
> If you do that then you probably don't care as much about translating 
> existing ATAGs from the bootloader and could as well just live with the 
> hardcoded values in the appended DTB.
> 

What I meant was you could translate these ATAGs into the DTB kernel
command-line options rather than come-up with something new. You already
having to mess with the command line.

Rob