Hi Linus, linus.walleij@xxxxxxxxxx wrote on Tue, 9 May 2023 20:30:33 +0200: > On Tue, May 9, 2023 at 9:31 AM Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote: > > linus.walleij@xxxxxxxxxx wrote on Sat, 06 May 2023 17:29:43 +0200: > > > > > This type of firmware partition appear in some devices in > > > NAND flash, so we need to be able to tag the partitions > > > with the appropriate type. > > > > > > The origin of the "SEAttle iMAge" is unknown. > > > > I don't see any kernel changes, why do we need an additional binding? > > The bindings are not strictly bound to Linux, it's more like all OS:es > uses the Linux DT binding repo because it is the biggest project. Yes, that's why I wanted more context :-) > Also we actually merge a bunch of bindings just to describe hardware > (or things like partitions), in the hope of making use of them in the > long run. It's always problematic to do it this way because no user == no precise requirement. As binding are supposed to remain stable, and because we, human are far from perfect when it comes to read the future, I of course prefer when there is an implementation that uses the new binding so we can more easily spot the issues. > Anyways, for the record, the full story: > > Currently this binding is used in out-of-tree OpenWrt code, where it > is used as magic for splitting partitions with mtdsplit. > > I guess you might be familiar with mtdsplit. It is a software partition > splitter that makes it possible to split a big partition into smaller > partitions dynamically, using magic block identifiers. > > The typical usecase is to put the kernel in the first flash blocks, > then pad up to the nearest even erase block, and then add a > JFFS2 or UBI filesystem immediately there. > > This way it avoids using static partitioning, the tools rebuilding the > firmware can dynamically split off more flash as the kernel image > grows. > > The mtdsplit code uses different magic numbers to identify where > the different partitions start. Is mtdsplit acting on a device or on a partition? Right now you define a partition to be compatible with seama, I would have imagined the partitions container should be compatible with seama instead of fixed-partitions, but I haven't looked at the whole implementation, so maybe my comment is just wrong. > One such type of partition is seama, so the code needs to know > that it should look for seama magic to determine the size and > split this partition in a kernel and rootfs part. This is the code: > https://git.openwrt.org/?p=openwrt/openwrt.git;a=tree;f=target/linux/generic/files/drivers/mtd/mtdsplit;h=3e0df856713a84b1decf17190f171cb10ce7a757;hb=HEAD That's very informative, thanks for all the context. I believe this could actually be part of the binding description (not the "this is an openWRT stuff", of course). > It is a bit sad that no-one has the energy to propose mtdsplit > upstream, I think it is quite generic and generally useful. I started > to make an upstream patch but got exhausted with the task. :-) Thanks, Miquèl
