On Mon, Feb 10, 2020 at 12:40:19PM +0100, Marek Szyprowski wrote: > Hi David, > > On 05.02.2020 06:45, David Gibson wrote: > > On Tue, Feb 04, 2020 at 01:58:44PM +0100, Marek Szyprowski wrote: > >> While applying dt-overlays using libfdt code, the order of the applied > >> properties and sub-nodes is reversed. This should not be a problem in > >> ideal world (mainline), but this matters for some vendor specific/custom > >> dtb files. This can be easily fixed by the little change to libfdt code: > >> any new properties and sub-nodes should be added after the parent's node > >> properties and subnodes. > >> > >> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > > I'm not convinced this is a good idea. > > > > First, anything that relies on the order of properties or subnodes in > > a dtb is deeply, fundamentally broken. That can't even really be a > > problem with a dtb file itself, only with the code processing it. > > I agree about the properties, but generally the order of nodes usually > implies the order of creation of some devices or objects. Huh? From the device tree client's point of view the devices just exist - the order of creation should not be visible to it. > This sometimes > has some side-effects. If those side effects matter, your code is broken. If you need to apply an order to nodes, you should be looking at 'reg' or other properties. > For comparison, the other lib used for fdt manipulation (libufdt) > applies overlays in a such way, that the order of properties and nodes > is not reversed. > > > I'm also concerned this could have a negative performance impact, > > since it has to skip over a bunch of existing things before adding the > > new one. On the other hand, that may be offset by the fact that it > > will reduce the amount of stuff that needs to be memmove()ed later on. > > This code is already slow (especially in the way the uboot's use it for > 'fdt apply' command), but in practice I've didn't observe negative > impact on the performance of applying large overlays at all. I'm going to need numbers, not just "I didn't see anything". -- 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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