On Sun, Mar 10, 2024 at 09:30:31AM +0100, Uwe Kleine-König wrote:
> Hello David,
>
> On Mon, Feb 26, 2024 at 04:53:53PM +1100, David Gibson wrote:
> > On Sun, Feb 25, 2024 at 06:54:23PM +0100, Uwe Kleine-König wrote:
> > > A phandle in an overlay is not supposed to overwrite a phandle that
> > > already exists in the base dtb as this breaks references to the
> > > respective node in the base.
> > >
> > > So add another iteration over the fdto that checks for such overwrites
> > > and fixes the fdto phandle's value to match the fdt's.
> > >
> > > A test is added that checks that newly added phandles and existing
> > > phandles work as expected.
> > >
> > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > > ---
> > > Hello,
> > >
> > > here comes the next iteration of the patch that fixes overlay
> > > application to not overwrite existing phandles.
> > >
> > > It is rebased to current main branch. The changes since v2 are:
> > >
> > > - Add documentation
> > > - Apply the simplification from 24f60011fd43 ("libfdt: Simplify
> > > adjustment of values for local fixups") in the functions added here.
> > > - Rename functions using shorter and better names
> > > - Changed the test device trees to yield a hole in the phandle space
> > > - Checked each phandle value not being overwritten separately
> > >
> > > Note I didn't switch the order of overlay_prevent_phandle_overwrite() and
> > > overlay_fixup_phandles() because the overlay's phandles must be resolved
> > > before I can do the recursion needed in
> > > overlay_prevent_phandle_overwrite().
> >
> > I'm not following what you mean here. IIUC, conflicts of the sort
> > you're handling can only arise when the overlay describes a phandle
> > for the target node of the reference - and therefore that target is in
> > the overlay. In that case all references to it in the overlay should
> > be encoded in __local_fixups__ rather than __fixups__. __fixups__, in
> > contrast describes references to nodes that aren't in the overlay, and
> > so can't be filled in - even with a tentative value - until the
> > overlay is applied.
> >
> > So, I'm not seeing how fixing these conflicts depends on resolution of
> > those "external" fixups, rather than just the "local" fixups. Am I
> > missing something?
>
> yupp, look at the overlay dts I added in tests/. It has
>
> &node_a {
> value = <32>;
> };
>
> which is translated to:
>
> fragment@1 {
> target = <0xffffffff>;
> __overlay__ {
> value = <0x00000020>;
> };
> };
> ...
> __fixups__ {
> node_a = ..., "/fragment@1:target:0"
> };
>
> Before I can recurse over fragment@1 and the matching base dtb node to
> check for phandle conflicts, I need /fragment@1:target resolved;
> otherwise I don't know where to look in the base dtb.
>
> So if I switch the order, fdtoverlay reports
>
> Failed to apply 'overlay_overlay_phandle.test.dtb': FDT_ERR_BADPHANDLE
>
> in make check.
Ah, right. It's specifically that we need to resolve the fragment
targets (including via external symbols) before we can resolve this.
Do you have a test case for this specific problem? If not, I'd be
worried, that I or someone else might forget the subtletey and try to
re-order at some point in the future.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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