[PATCH 15/15] HiFive1: disable/enable interrupts during context switch

[Denis Obrezkov]

2017-08-17 22:07 GMT+02:00 Gedare Bloom <gedare at rtems.org>:

> On Thu, Aug 17, 2017 at 1:48 PM, Denis Obrezkov <denisobrezkov at gmail.com>
> wrote:
> > 2017-08-17 17:25 GMT+02:00 Gedare Bloom <gedare at rtems.org>:
> >>
> >> On Wed, Aug 16, 2017 at 11:13 AM, Denis Obrezkov
> >> <denisobrezkov at gmail.com> wrote:
> >> > ---
> >> >  cpukit/score/cpu/riscv32/riscv-context-switch.S | 12 ++++++++++--
> >> >  1 file changed, 10 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/cpukit/score/cpu/riscv32/riscv-context-switch.S
> >> > b/cpukit/score/cpu/riscv32/riscv-context-switch.S
> >> > index a199596..bcdfe0e 100644
> >> > --- a/cpukit/score/cpu/riscv32/riscv-context-switch.S
> >> > +++ b/cpukit/score/cpu/riscv32/riscv-context-switch.S
> >> > @@ -46,6 +46,7 @@ PUBLIC(restore)
> >> >
> >> >  SYM(_CPU_Context_switch):
> >> >    /* Disable interrupts and store all registers */
> >> > +  csrci mstatus, 0x8
> >> Why is this necessary?
> >>
> >> >    SREG x1, 4(a0)
> >> >    SREG x2, 8(a0)
> >> >    SREG x3, 12(a0)
> >> > @@ -78,8 +79,9 @@ SYM(_CPU_Context_switch):
> >> >    SREG x30, 120(a0)
> >> >    SREG x31, 124(a0)
> >> >
> >> > -SYM(restore):
> >> >
> >> > +SYM(restore):
> >> > +
> >> >    LREG x1, 4(a1)
> >> >    LREG x2, 8(a1)
> >> >    LREG x3, 12(a1)
> >> > @@ -111,9 +113,15 @@ SYM(restore):
> >> >    LREG x29, 116(a1)
> >> >    LREG x30, 120(a1)
> >> >    LREG x31, 124(a1)
> >> > -       ret
> >> > +
> >> > +
> >> > +  csrsi mstatus, 0x8
> >> > +  nop
> >> > +  nop
> >> Why the nops?
> >>
> >> > +  ret
> >> >
> >> >  SYM(_CPU_Context_restore):
> >> > +  csrci mstatus, 0x8
> >> >    mv     a1, a0
> >> >    j       restore
> >> >    nop
> >> > --
> >> > 2.1.4
> >> >
> >> > _______________________________________________
> >> > devel mailing list
> >> > devel at rtems.org
> >> > http://lists.rtems.org/mailman/listinfo/devel
> >
> > So, don't we turn off interrupts during the context switch?
>
> Nope, and turning them back on unconditionally is wrong too.
>
> > Yes, nops are unnecessary.
> >
> >
> > --
> > Regards, Denis Obrezkov
>
Ok, I was confused by this obsolete comment:
/* Disable interrupts and store all registers */
Will remove all that enabling/disabling.

Is the same true for start.S file with interrupted task's stack saving?



-- 
Regards, Denis Obrezkov
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