On Wed, Aug 1, 2018 at 10:55 AM, Palmer Dabbelt <pal...@sifive.com> wrote: > On Tue, 26 Jun 2018 21:22:26 PDT (-0700), alan...@andestech.com wrote: >> >> This patch adds an option, CONFIG_FPU, to enable/disable floating >> procedures. Also, some style issues are fixed. >> >> Signed-off-by: Alan Kao <alan...@andestech.com> >> Cc: Greentime Hu <greent...@andestech.com> >> Cc: Zong Li <z...@andestech.com> >> --- >> arch/riscv/Kconfig | 9 ++++ >> arch/riscv/Makefile | 19 +++---- >> arch/riscv/include/asm/switch_to.h | 6 +++ >> arch/riscv/kernel/entry.S | 3 +- >> arch/riscv/kernel/process.c | 7 ++- >> arch/riscv/kernel/signal.c | 82 +++++++++++++++++++++--------- >> 6 files changed, 90 insertions(+), 36 deletions(-) >> >> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig >> index 6debcc4afc72..6069597ba73f 100644 >> --- a/arch/riscv/Kconfig >> +++ b/arch/riscv/Kconfig >> @@ -232,6 +232,15 @@ config RISCV_BASE_PMU >> >> endmenu >> >> +config FPU >> + bool "FPU support" >> + default y >> + help >> + Say N here if you want to disable all floating-point related >> procedure >> + in the kernel. >> + >> + If you don't know what to do here, say Y. >> + >> endmenu > > > Sorry for letting this slide for a bit. While I'm not opposed to a solution > that requires a FPU Kconfig option, it'd be a bit better if we could detect > this at boot time. I think this should be possible because at one point > this actually worked and we could boot the same kernel on FPU and no-FPU > systems.
I believe it would suffice to have start_thread set sstatus.FS to OFF for no-FPU systems (vs. INITIAL for systems with FPU). The ISA string in the devicetree should indicate whether F/D extensions are present. That said, it makes sense to me to additionally provide the Kconfig option. This would elide the sstatus.SD check for no-FPU systems, shaving a couple instructions off the context-switch path. It would also enable mimicking the behavior of a no-FPU system even when the FPU is present. > > If that's not possible then we'll have to take something like this. There > were some comments on this v2 but I don't see a v3, did I miss one?
