On 07/13/16 at 10:34am, Mark Rutland wrote: > On Wed, Jul 13, 2016 at 10:36:14AM +0800, Dave Young wrote: > > But consider we can kexec to a different kernel and a different initrd so there > > will be use cases to pass a total different dtb as well. > > It depends on what you mean by "a different kernel", and what this > implies for the DTB. > I thought about kexec as a boot loader just like other bootloaders. So just like a normal boot kexec should also accept external dtb. But acutally kexec is different because it can get original dtb and use it. So I agreed if we can not find a real use case that we have to extend it we should keep current interface. > I expect future arm64 Linux kernels to function with today's DTBs, and > the existing boot protocol. The kexec_file_load syscall already has > enough information for the kernel to inject the initrd and bootargs > properties into a DTB. > > In practice on x86 today, kexec_file_load only supports booting to a > Linux kernel, because the in-kernel purgatory only implements the x86 > Linux boot protocol. Analagously, for arm64 I think that the first > kernel should use its internal copy of the boot DTB, with /chosen fixed > up appropriately, assuming the next kernel is an arm64 Linux image. > > If booting another OS, the only parts of the DTB I would expect to > change are the properties under chosen, as everything else *should* be > OS-independent. However the other OS may have a completely different > boot protocol, might not even take a DTB, and will likely need a > compeltely different purgatory implementation. So just allowing the DTB > to be altered isn't sufficient for that case. > > There might be cases where we want a different DTB, but as far as I can > tell we have nothing analagous on x86 today. If we do need this, we > should have an idea of what real case(s) were trying to solve. Agreed. Thanks Dave
