Hi Pantelis, On Fri, Nov 9, 2012 at 2:13 AM, Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote: >>>> Option C: U-Boot loads both the base and overlay FDT files, merges them, >>>> and passes the resolved tree to the kernel. >>>> >>> >>> Could be made to work. Only really required if Joanne wants the >>> cape interface to work for u-boot too. For example if the cape has some >>> kind of network interface that u-boot will use to boot from. >>> >> >> I love Grant's hashing idea a lot keeping the phandle problem for >> compile time and not requiring fixups. >> >> IMO it is still a cleaner approach if u-boot does the tree merging for >> all cases, and not the kernel. >> >> That way from a development standpoint, very little or nothing will >> have to be changed in kernel (except for scripts/dtc) considering we >> are moving forward with hashing. >> >> Also this discussed a while back but at some point is going to brought >> up again- loading of dt fragment directly from EEPROM and merging at >> run time. If we were to implement this in kernel, we would have to add >> cape specific EEPROM reading code, merge the tree before it is >> unflattened and parse. I think doing tree merging in kernel is messy >> and we should do it in uboot. Ideally reading the fragment from the >> EEPROM for all capes and merging without worrying about version >> detection, Doing the merge and passing the merged blob to the kernel >> which (kernel) works the same way it does today. > > Not going to work, for a lot of cases. Doing it in the kernel seems to be > the cleaner option. There are valid use cases for doing in u-boot too. True, if dynamic runtime stuff from userspace is what we're talking about, then yeah I see the important need for kernel to do the merge. >> Alternatively to hashing, reading david gibsons paper I followed, >> phandle is supposed to 'uniquely' identity node. I wonder why the node >> name itself is not sufficient to unquiely identify. The code that does >> the tree walking can then just strcmp the node name while it walks the >> tree instead of having to find a node with a phandle number. I guess >> the reason is phandles are small to store as data values. Another >> approach can be to arrange the string block in alphabetical order >> (unless it already is), and store phandle as index of the node name >> referenced relative to the starting of the strong block. This will not >> affect nodes in dtb being moved around since they will still have the >> same index value. the problem being adding or removing nodes Changes >> the offsets of all other nodes in the string block as well.. Hmm. >> > > This is pretty radical change to the DT format, no? Yes, true and the only way hypothetically to replace the phandle tree-walking mechanism is to store node paths instead of phandle which David pointed is too long to store, so I guess this wont work after all. Anyway this was an interesting exercise, thanks. Regards, Joel -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html