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

[Nicolas Pitre]

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 at linaro.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.


Nicolas