On Tue, 16 May 2017 14:19:47 +0530
"Gautham R. Shenoy" <e...@linux.vnet.ibm.com> wrote:
> From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
>
> On Power9 DD1 due to a hardware bug the Power-Saving Level Status
> field (PLS) of the PSSCR for a thread waking up from a deep state can
> under-report if some other thread in the core is in a shallow stop
> state. The scenario in which this can manifest is as follows:
>
> 1) All the threads of the core are in deep stop.
> 2) One of the threads is woken up. The PLS for this thread will
> correctly reflect that it is waking up from deep stop.
> 3) The thread that has woken up now executes a shallow stop.
> 4) When some other thread in the core is woken, its PLS will reflect
> the shallow stop state.
>
> Thus, the subsequent thread for which the PLS is under-reporting the
> wakeup state will not restore the hypervisor resources.
>
> Hence, on DD1 systems, use the Requested Level (RL) field as a
> workaround to restore the contents of the hypervisor resources on the
> wakeup from the stop state.
>
> Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> ---
> arch/powerpc/include/asm/paca.h | 2 ++
> arch/powerpc/kernel/asm-offsets.c | 1 +
> arch/powerpc/kernel/idle_book3s.S | 13 ++++++++++++-
> 3 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index 1c09f8f..77f60a0 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -177,6 +177,8 @@ struct paca_struct {
> * to the sibling threads' paca.
> */
> struct paca_struct **thread_sibling_pacas;
> + /* The PSSCR value that the kernel requested before going to stop */
> + u64 requested_psscr;
> #endif
>
> #ifdef CONFIG_PPC_STD_MMU_64
> diff --git a/arch/powerpc/kernel/asm-offsets.c
> b/arch/powerpc/kernel/asm-offsets.c
> index 709e234..e15c178 100644
> --- a/arch/powerpc/kernel/asm-offsets.c
> +++ b/arch/powerpc/kernel/asm-offsets.c
> @@ -742,6 +742,7 @@ int main(void)
> OFFSET(PACA_THREAD_MASK, paca_struct, thread_mask);
> OFFSET(PACA_SUBCORE_SIBLING_MASK, paca_struct, subcore_sibling_mask);
> OFFSET(PACA_SIBLING_PACA_PTRS, paca_struct, thread_sibling_pacas);
> + OFFSET(PACA_REQ_PSSCR, paca_struct, requested_psscr);
> #endif
>
> DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);
> diff --git a/arch/powerpc/kernel/idle_book3s.S
> b/arch/powerpc/kernel/idle_book3s.S
> index 6c9920d..98a6d07 100644
> --- a/arch/powerpc/kernel/idle_book3s.S
> +++ b/arch/powerpc/kernel/idle_book3s.S
> @@ -379,6 +379,7 @@ _GLOBAL(power9_idle_stop)
> mfspr r5,SPRN_PSSCR
> andc r5,r5,r4
> or r3,r3,r5
> + std r3, PACA_REQ_PSSCR(r13)
> mtspr SPRN_PSSCR,r3
> LOAD_REG_ADDR(r5,power_enter_stop)
> li r4,1
> @@ -498,12 +499,22 @@ pnv_restore_hyp_resource_arch300:
> LOAD_REG_ADDRBASE(r5,pnv_first_deep_stop_state)
> ld r4,ADDROFF(pnv_first_deep_stop_state)(r5)
>
> - mfspr r5,SPRN_PSSCR
> +BEGIN_FTR_SECTION_NESTED(71)
> + /*
> + * Assume that we are waking up from the state
> + * same as the Requested Level (RL) in the PSSCR
> + * which are Bits 60-63
> + */
> + ld r5,PACA_REQ_PSSCR(r13)
> + rldicl r5,r5,0,60
> +FTR_SECTION_ELSE_NESTED(71)
> /*
> * 0-3 bits correspond to Power-Saving Level Status
> * which indicates the idle state we are waking up from
> */
> + mfspr r5, SPRN_PSSCR
> rldicl r5,r5,4,60
> +ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_POWER9_DD1, 71)
> cmpd cr4,r5,r4
> bge cr4,pnv_wakeup_tb_loss /* returns to caller */
>
