Hello Arnd, On Mon, Feb 27, 2023 at 03:58:50PM +0100, Arnd Bergmann wrote: > On Mon, Feb 27, 2023, at 15:28, Dmitry Rokosov wrote: > > Hello Neil! > > > > On Mon, Feb 27, 2023 at 09:15:04AM +0100, neil.armstrong@xxxxxxxxxx wrote: > > > > [...] > > > >> I'm aware Amlogic also runs their kernel as 32bit to gain a few kbytes > >> of memory, but those processors are ARMv8 and the arm64 arch code > >> has been designed for those CPUs. > >> > >> So far I didn't find a single good reason to add 32bit support for > >> ARMv8 Amlogic based SoCs, if you have a solid reason please share. > > > > I totally agree with you, but I suppose it's fully related to 'big' > > Amlogic SoC like S905_ or A311_ series. A113L (aka 'a1') is > > a cost-efficient dual-core SoC which is used for small, cheap solutions > > with cheap components. Every cent is important during BoM development. > > That's why usually ODMs install small ROM and RAM capacity, and each > > megabyte is important for RAM/ROM kernel and rootfs footprints. > > Why am I talking about rootfs? For such small projects a good > > choice is buildroot rootfs assembling framework. Unfortunatelly, > > buildroot doesn't support 'compat' mode when kernel and userspace have > > a different bitness. In the internal project, we save several > > percents of ROM/RAM free space using 32-bit configuration (mostly rootfs > > ROM space, to be honest). Therefore, for such 'little' cost-efficient > > SoCs we can make an exception and support 32-bit configuration, from my > > point of view. > > > > What do you think about that? > > I would argue that is a problem with buildroot, and using a 32-bit > kernel is not something we should encourage over fixing buildroot > to do it right, or building the kernel separately from the rootfs. > > We do allow building support for a couple of ARMv8 SoCs in 32-bit > mode, but that is usually because they ship with a 32-bit bootrom > and cannot actually run a 64-bit kernel. To be honest, I didn't know about this principle. It looks like a very rational approach "start from max supported bitness". Based on overall maintainers opinion, we have to prepare a patch for buildroot to support compat mode :) [...] -- Thank you, Dmitry
