On Wed, Aug 1, 2018 at 10:55 AM, Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:
On Tue, 26 Jun 2018 21:22:26 PDT (-0700), alankao@xxxxxxxxxxxxx wrote:
This patch adds an option, CONFIG_FPU, to enable/disable floating
procedures. Also, some style issues are fixed.
Signed-off-by: Alan Kao <alankao@xxxxxxxxxxxxx>
Cc: Greentime Hu <greentime@xxxxxxxxxxxxx>
Cc: Zong Li <zong@xxxxxxxxxxxxx>
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
@@ -232,6 +232,15 @@ config RISCV_BASE_PMU
+ bool "FPU support"
+ default y
+ Say N here if you want to disable all floating-point related
+ in the kernel.
+ If you don't know what to do here, say Y.
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
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
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?