Hi Ludwig, On Mon, 11 May 2026 at 05:18, Ludwig Nussel <[email protected]> wrote: > > On 5/7/26 17:33, Simon Glass wrote: > > On Wed, 6 May 2026 at 09:29, Ludwig Nussel <[email protected]> > > wrote: > >> > >> On 5/4/26 14:26, Simon Glass wrote: > >>> On 2026-04-30T12:25:59, Ludwig Nussel <[email protected]> wrote: > >>>> qemu: overlay signature nodes > >>>> [...] > >>>> diff --git a/board/emulation/qemu-arm/qemu-arm.c > >>>> b/board/emulation/qemu-arm/qemu-arm.c > >>>> @@ -147,7 +147,38 @@ int dram_init_banksize(void) > >>>> int board_fdt_blob_setup(void **fdtp) > >>>> { > >>>> /* QEMU loads a generated DTB for us at the start of RAM. */ > >>>> - *fdtp = (void *)CFG_SYS_SDRAM_BASE; > >>>> + void *qemu_fdt = (void *)CFG_SYS_SDRAM_BASE; > >>>> + int ret; > >>>> + > >>>> + if (!*fdtp) > >>>> + goto out; > >>> > >>> This runs the opposite direction to qemu-sbsa, which uses the U-Boot > >>> DT as the base and overlays the QEMU DT onto it (see > >>> fdtdec_board_setup() in board/emulation/qemu-sbsa/qemu-sbsa.c). Done > >>> this way, any node in U-Boot's built-in DT that shares a name with a > >>> QEMU node (/cpus, /memory, /chosen, ...) will have its properties > >>> merged into QEMU's, potentially clobbering the hardware description. > >>> If this is correct, please explain in the commit message why the merge > >>> runs in this direction. > >> > >> IIUC the FDT patching happens before relocation. QEMU starts u-boot from > >> a ROM at address 0 so writing to the embedded DT does not work. QEMU's > >> provided DT is at a writable RAM location so patching that one works. > >> > >> I don't know which direction makes more sense really. If you say merging > >> QEMU's DT into U-Boot's is better then board_fix_fdt() could be used for > >> the merging I guess. Looks like that could work with > >> CONFIG_OF_INITIAL_DTB_READONLY and CONFIG_OF_BOARD_FIXUP set. > > > > Hmmm now I am wondering how this actually works with sbsa. As you > > point out it's hard to see how the fdtdec_board_setup() works before > > relocation...I don't have the energy to dig into it, though. > > AFAICS SBSA relocates u-boot into RAM via > arch/arm/include/asm/arch-qemu-sbsa/boot0.h on startup.
Ah OK, well anyway what you have seems OK to me. Let's see how it goes down the track. Regards, SImon
