On Wed, Nov 21, 2018 at 9:58 PM Palmer Dabbelt <pal...@sifive.com> wrote: > > On Tue, 20 Nov 2018 19:41:10 PST (-0800), a...@brainfault.org wrote: > > This patch adds kconfig option RISCV_SMODE to run u-boot in > > S-mode. When this opition is enabled we use s<xyz> CSRs instead > > of m<xyz> CSRs. > > > > It is important to note that there is no equivalent S-mode CSR > > for misa and mhartid CSRs so we expect M-mode runtime firmware > > (BBL or equivalent) to emulate misa and mhartid CSR read. > > > > In-future, we will have more patches to avoid accessing misa and > > mhartid CSRs from S-mode. > > Ya, I don't like this. Our current boot protocol puts mhartid in a1 upon > entering the supervisor, and allows the detection of misa via a device tree > pointer provided in a0. > > As long as everyone agrees this isn't what we're actually looking for then I'm > fine with the patch, I just don't want to end up requiring this "M mode > emulates some CSRs for S mode" interface. Since we don't have an actual > platform spec we've got to be careful to avoid a bunch of defacto interfaces > that we'll need to support later.
Yes, it's a temporary thingy to emulate misa and mhartid in BBL. Eventually, U-Boot will be fixed to avoid direct access of misa and mhartid. Regards, Anup _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
