[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 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 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.
> > 
> 
> 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.

Agreed.  What I meant is that you're unlikely to use the kernel built-in 
command line if you care about this.


Nicolas