Hi Sahil,
Am 2022-01-06 07:09, schrieb Sahil Malhotra (OSS):
I don't know I follow. u-boot and linux should have the same device tree; regardless if that device is used or not. So applying the overlay just for linux isn't enough here.
Ok, I don't think that as of now, in all platforms uboot and linux have same devie tree.
That doesn't mean it is ok to diverge again. I put a lot of effort in syncing uboot's LS1028A device tree with linux.
But I will try to address your concern, but I don’t know how to apply overlay to dtb which is embedded in u-boot binary, Can you please point me to one reference which is doing this thing, I will take reference from there.
Sorry I can't advise you with that. There is board_fix_fdt() maybe that will help. But I'm not conviced this is the correct approach, see below.
We don't use DTB in OP-TEE, but when we use CAAM in OP-TEE, OP-TEE reserves One Job Ring for its use and that is communicated to Kernel using DTB overlay.
what if the overlay doesn't match the dtb?
I didn't get this point, can you please elaborate a little.
You are merging a dtb fragment with an unknown dtb, right? Who says they match? you might have an old dtb where the supplied dtb fragment doesn't make any sense.
I might be missing something here. Eg. where is the linux dtb supposed to come from? This patchset is really missing an example and a description how things should work.
If supplied DTB does not match with DTB overlay fragment. then overlay will not get applied.
I don't think this is what happens here. fdt_overlay_apply() will mark the fdt as damaged and there will be no fdt at all.
We don't have any control on where user picks the DTB, but we can only make sure DTB overlay feature must work with DTBs which are upstreamed If user makes its own customized DTB, we cannot make sure that things will work.
Again. Is there any documentation on how this should all work together? Where does optee get its device tree from? Shouldn't it be the same device tree as u-boot and linux? Shouldn't optee modify the device tree in place before jumping back to u-boot?
Andrey, do you know how this works on imx?
-michael