Hi Tom, On Fri, 11 Jul 2025 at 11:45, Tom Rini <tr...@konsulko.com> wrote: > > On Fri, Jul 04, 2025 at 06:42:05AM -0700, Raymond Mao wrote: > > > During FDT setup, apply all existing DT overlays from the bloblist > > to the base FDT if bloblist is being used for handoff from previous > > boot stage. > > According to the spec update for DT overlay handoff[1], an overlay > > must have the same top-level compatible string as its target base > > DT has. > > Before applying the DTO, it checks whether sufficient space is > > reserved in the base FDT region. A margin (0x400) is used during > > estimating the space size required by the merged DT. > > A resizing happens if the reserved space is insufficient. > > After all overlays are applied, it resizes to the actual size of the > > merged DT. > > Note that the margin (0x400) is arbitrary from experience, it might > > not cover all possible scenarios as complex overlays with many > > properties might require extra spaces and lead to FDT_ERR_NOSPACE > > error. > > > > [1] Add Transfer Entry for Devicetree Overlay > > https://github.com/FirmwareHandoff/firmware_handoff/pull/74 > [snip] > > + actual_size = fdt_totalsize(*blob); > > + /* Add margin for extra size growth after merging */ > > + new_fdt_size = fdt_totalsize(live_fdt) + actual_size + 0x400; > > This is still a fixed value and still not the right way to handle it. I > think now that we expose configuring the amount of extra space we have > for the tree it should possibly even just fail out with an error message > that points to SYS_FDT_PAD? > Shall we do it following the steps below? 1. Expand to "fdt_totalsize() + SYS_FDT_PAD" without conditions. 2. Apply each overlay and out if any errors are returned. 3. Shrink to fdt_totalsize().
In this case, the expansion is only once at the beginning. Is it good? Regards, Raymond > -- > Tom
