[PATCH-V2 1/1] sparc: Fix context switch on SMP

[Sebastian Huber]

On 16/11/15 13:14, Daniel Cederman wrote:
> I was unsure if the ET bit was always set or not for newly created 
> task contexts, or if this was the first place that traps got enabled 
> for a new task. If it is always set we can remove that instruction.

The PSR is initialized like this (_CPU_Context_Initialize()):

[...]
     /*
      *  Build the PSR for the task.  Most everything can be 0 and the
      *  CWP is corrected during the context switch.
      *
      *  The EF bit determines if the floating point unit is available.
      *  The FPU is ONLY enabled if the context is associated with an FP 
task
      *  and this SPARC model has an FPU.
      */

     sparc_get_psr( tmp_psr );
     tmp_psr &= ~SPARC_PSR_PIL_MASK;
     tmp_psr |= (new_level << 8) & SPARC_PSR_PIL_MASK;
     tmp_psr &= ~SPARC_PSR_EF_MASK;      /* disabled by default */

#if (SPARC_HAS_FPU == 1)
     /*
      *  If this bit is not set, then a task gets a fault when it accesses
      *  a floating point register.  This is a nice way to detect floating
      *  point tasks which are not currently declared as such.
      */

     if ( is_fp )
       tmp_psr |= SPARC_PSR_EF_MASK;
#endif
     the_context->psr = tmp_psr;
[...]

Since traps must be enabled at C level, this should be fine.

Maybe add this to the patch for documentation purposes:

diff --git a/cpukit/score/cpu/sparc/cpu.c b/cpukit/score/cpu/sparc/cpu.c
index 569b6f8..5434355 100644
--- a/cpukit/score/cpu/sparc/cpu.c
+++ b/cpukit/score/cpu/sparc/cpu.c
@@ -356,6 +356,9 @@ void _CPU_Context_Initialize(
      tmp_psr |= (new_level << 8) & SPARC_PSR_PIL_MASK;
      tmp_psr &= ~SPARC_PSR_EF_MASK;      /* disabled by default */

+    /* _CPU_Context_restore_heir() relies on this */
+    _Assert( ( tmp_psr & SPARC_PSR_ET_MASK ) != 0 );
+
  #if (SPARC_HAS_FPU == 1)
      /*
       *  If this bit is not set, then a task gets a fault when it accesse

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.