Hi Joel, Again, sorry for the late reply due to travel. On Nov 10, 2012, at 5:36 AM, Joel A Fernandes wrote: > 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. > Kernel doing the merge is our use case, and I feel it's the use case of about 90% of users. u-boot doing the merge is the rest. >>> 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. > It is always nice to have a fresh perspective. Thank you. > Regards, > Joel Regards -- Pantelis -- 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
