On Fri, Aug 29, 2014 at 6:13 AM, Grant Likely <grant.lik...@linaro.org> wrote:
> On 29 Aug 2014 02:56, "Michael Ellerman" <m...@ellerman.id.au> wrote:
>>
>> On Thu, 2014-08-28 at 09:27 -0500, Rob Herring wrote:
>> > On Thu, Aug 28, 2014 at 3:40 AM, Michael Ellerman <m...@ellerman.id.au>
>> > wrote:
>> > > In commit e6a6928c3ea1 "of/fdt: Convert FDT functions to use libfdt",
>> > > the kernel stopped supporting old flat device tree formats. The minimum
>> > > supported version is now 0x10.
>> >
>> > Ugg. Is that something which needs to be supported? Supporting it at
>> > this point would mean adding support to libfdt.
>>
>> Well it would have been nice to keep supporting v2, dropping it broke
>> kexec-tools for example. But it's done now, so we'll just deal with the
>> fallout.
>
> Umm, so we broke userspace? That's not okay. At the very least we
> should investigate how much work is needed to bring v2 support into
> libfdt, or up-rev the flat tree at runtime before we parse it.
Would up-reving work? kexec-tools is broken or booting a new kernel
with kexec is broken?
> We should be able to update it in-line. IIRC, the main difference
> between v2 and v0x10 is that only the leaf node name is encoded into
> the node instead of the full name. We can loop over the tree and
> truncate all the names while filling the unused bytes with FDT NOP
> tags. Should be simple. Something like the following:
There is also the name property in v1-v3. I'm guessing linux ignores
that already?
>
> fixup_old_device_tree(blob)
> {
> for (offset = fdt_next_node(blob, -1, &depth);
> offset >= 0 && depth >= 0 && !rc;
> offset = fdt_next_node(blob, offset, &depth)) {
> char *pathp = fdt_get_name(blob, offset, NULL);
> if (*pathp == '/') {
> char *leaf = kbasename(pathp);
> int len = strlen(pathp);
> int newlen = strlen(leaf);
> strcpy(pathp, leaf); /* copying in place, need
> to check make sure this code is safe */
> node->size = newlen /* fixme - this is just
> pseudocode */
> newlen = FDT_TAGALIGN(newlen);
> while (newlen < len) {
> *(pathp + newlen) = FDT_NOP;
> newlen = FDT_TAGALIGN(newlen+1);
> }
> }
> }
>
> }
>
> There's probable some more elegance that can be put into the above
> block, but you get the idea. That could be run in-place without
> copying the tree to another location, and it could possibly be done in
> the boot wrapper. Then we'd also be able to get rid of the v2
> compatibility code elsewhere in drivers/of/fdt.c because it would
> already be taken care of.
That's what got us into this problem. ;)
Rob
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