[PATCH] SPARC32 : WIM register update delay

[Olivier DANET]

The SparcV8 standard states, page 134 : 
"If any of the three instructions after a write state register instruction reads any field
 that was changed by the original write state register instruction, the contents of that
 field read by that instruction are undefined."
The restore instruction depends on the %WIM register, three NOPs must be inserted.

diff a/openbios-devel/arch/sparc32/wuf.S b/openbios-devel/arch/sparc32/wuf.S
--- a/openbios-devel/arch/sparc32/wuf.S
+++ b/openbios-devel/arch/sparc32/wuf.S
@@ -121,7 +121,7 @@ fnwin_patch1:       srl     %t_wim, 7, %twin_tmp2
 fnwin_patch2:  and     %twin_tmp1, 0xff, %twin_tmp1

wr      %twin_tmp1, 0x0, %wim   /* Make window 'I' invalid */
-
+    WRITE_PAUSE
        restore %g0, %g0, %g0           /* Restore to window 'O' */

/* Trapped from kernel, we trust that the kernel does not

Signed-off-by: Olivier DANET

[Blue Swirl]

On Tue, Jan 22, 2013 at 9:33 PM, Olivier DANET  wrote:
> The SparcV8 standard states, page 134 :
> "If any of the three instructions after a write state register instruction reads any field
>  that was changed by the original write state register instruction, the contents of that
>  field read by that instruction are undefined."
> The restore instruction depends on the %WIM register, three NOPs must be inserted.

Please put the SoB here.
> diff a/openbios-devel/arch/sparc32/wuf.S b/openbios-devel/arch/sparc32/wuf.S
> --- a/openbios-devel/arch/sparc32/wuf.S
> +++ b/openbios-devel/arch/sparc32/wuf.S
> @@ -121,7 +121,7 @@ fnwin_patch1:       srl     %t_wim, 7, %twin_tmp2
>  fnwin_patch2:  and     %twin_tmp1, 0xff, %twin_tmp1
>     wr      %twin_tmp1, 0x0, %wim   /* Make window 'I' invalid */
> WRITE_PAUSE

As you cite, this is needed on real HW. QEMU does not need it since
internal pipelines are not modeled. Perhaps this (or the definition of
WRITE_PAUSE) should be surrounded by
#ifndef CONFIG_QEMU
#endif

Anyway, TCG optimizes the nops away so it doesn't matter.
>     restore %g0, %g0, %g0           /* Restore to window 'O' */
>
>     /* Trapped from kernel, we trust that the kernel does not
>
> Signed-off-by: Olivier DANET

[Blue Swirl]

Thanks, applied.

On Tue, Jan 22, 2013 at 9:33 PM, Olivier DANET  wrote:
> The SparcV8 standard states, page 134 :
> "If any of the three instructions after a write state register instruction reads any field
>  that was changed by the original write state register instruction, the contents of that
>  field read by that instruction are undefined."
> The restore instruction depends on the %WIM register, three NOPs must be inserted.
>
> diff a/openbios-devel/arch/sparc32/wuf.S b/openbios-devel/arch/sparc32/wuf.S
> --- a/openbios-devel/arch/sparc32/wuf.S
> +++ b/openbios-devel/arch/sparc32/wuf.S
> @@ -121,7 +121,7 @@ fnwin_patch1:       srl     %t_wim, 7, %twin_tmp2
>  fnwin_patch2:  and     %twin_tmp1, 0xff, %twin_tmp1
>     wr      %twin_tmp1, 0x0, %wim   /* Make window 'I' invalid */
>
> WRITE_PAUSE
>    restore %g0, %g0, %g0           /* Restore to window 'O' */
>
> /* Trapped from kernel, we trust that the kernel does not
>
> Signed-off-by: Olivier DANET