On Fri, Aug 03, 2018 at 09:03:00PM -0700, Palmer Dabbelt wrote: > On Wed, 01 Aug 2018 11:23:43 PDT (-0700), Andrew Waterman wrote: > >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. > > That sounds like a good argument. Do you mind submitting a two-part patch > set, to: > > * Allow FPU kernels to detect and run correctly on non-FPU systems. You > should be able to detect these very early by writing to sstatus, or later > by looking at the device tree. > * Add a Kconfig option to disable the FPU entirely (which is pretty much > this patch). > > Thanks! >
Thanks for the feedback from all of you. We will fix v3 according to Christph's suggestions, and append a new patch of the auto-detecting feature.
