On Sun,  6 Aug 2017 03:02:41 +1000
Nicholas Piggin <npig...@gmail.com> wrote:

> When stop is executed with EC=ESL=0, it appears to execute like a
> normal instruction (resuming from NIP when woken by interrupt).
> So all the save/restore handling can be avoided completely. In
> particular NV GPRs do not have to be saved, and MSR does not have
> to be switched back to kernel MSR.
> 
> So move the test for "lite" sleep states out to power9_idle_stop.

I forgot to mention this actually breaks in the simulator because
it sets MSR as though it's taken a system reset interrupt when
resuming from EC=0 stop. It works on real hardware.

This might have to be quirked away by firmware or something, but
I've reported the bug so waiting to hear back first.

Thanks,
Nick

> 
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
>  arch/powerpc/kernel/idle_book3s.S | 38 +++++++++++++-------------------------
>  1 file changed, 13 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/idle_book3s.S 
> b/arch/powerpc/kernel/idle_book3s.S
> index 8ac366a51bb5..9eb47c99dc39 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -251,31 +251,8 @@ enter_winkle:
>  /*
>   * r3 - PSSCR value corresponding to the requested stop state.
>   */
> -power_enter_stop:
> -/*
> - * Check if we are executing the lite variant with ESL=EC=0
> - */
> -     andis.   r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
> +power_enter_stop_esl:
>       clrldi   r3,r3,60 /* r3 = Bits[60:63] = Requested Level (RL) */
> -     bne      .Lhandle_esl_ec_set
> -     PPC_STOP
> -     li      r3,0  /* Since we didn't lose state, return 0 */
> -
> -     /*
> -      * pnv_wakeup_noloss() expects r12 to contain the SRR1 value so
> -      * it can determine if the wakeup reason is an HMI in
> -      * CHECK_HMI_INTERRUPT.
> -      *
> -      * However, when we wakeup with ESL=0, SRR1 will not contain the wakeup
> -      * reason, so there is no point setting r12 to SRR1.
> -      *
> -      * Further, we clear r12 here, so that we don't accidentally enter the
> -      * HMI in pnv_wakeup_noloss() if the value of r12[42:45] == WAKE_HMI.
> -      */
> -     li      r12, 0
> -     b       pnv_wakeup_noloss
> -
> -.Lhandle_esl_ec_set:
>       /*
>        * POWER9 DD2 can incorrectly set PMAO when waking up after a
>        * state-loss idle. Saving and restoring MMCR0 over idle is a
> @@ -348,9 +325,20 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66); 
>         \
>   * r3 contains desired PSSCR register value.
>   */
>  _GLOBAL(power9_idle_stop)
> +     /*
> +      * Check if we are executing the lite variant with ESL=EC=0
> +      * This case resumes execution after the stop instruction without
> +      * losing any state, so nothing has to be saved.
> +      */
> +     andis.  r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
> +     bne     1f
> +     PPC_STOP
> +     li      r3,0  /* Since we didn't lose state, return 0 */
> +     blr
> +1:   /* state-loss idle */
>       std     r3, PACA_REQ_PSSCR(r13)
>       mtspr   SPRN_PSSCR,r3
> -     LOAD_REG_ADDR(r4,power_enter_stop)
> +     LOAD_REG_ADDR(r4,power_enter_stop_esl)
>       b       pnv_powersave_common
>       /* No return */
>  

Reply via email to