Re: [PATCH 2/2] powerpc/powernv/idle: save-restore DAWR0,DAWRX0 for P10

[Pratik Sampat]

On 09/07/20 2:39 pm, Gautham R Shenoy wrote:

On Fri, Jul 03, 2020 at 06:16:40PM +0530, Pratik Rajesh Sampat wrote:

Additional registers DAWR0, DAWRX0 may be lost on Power 10 for
stop levels < 4.

Adding Ravi Bangoria <ravi.bango...@linux.ibm.com> to the cc.

Therefore save the values of these SPRs before entering a  "stop"
state and restore their values on wakeup.

Signed-off-by: Pratik Rajesh Sampat <psam...@linux.ibm.com>

The saving and restoration looks good to me.

---
  arch/powerpc/platforms/powernv/idle.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/idle.c 
b/arch/powerpc/platforms/powernv/idle.c
index 19d94d021357..471d4a65b1fa 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -600,6 +600,8 @@ struct p9_sprs {
        u64 iamr;
        u64 amor;
        u64 uamor;
+       u64 dawr0;
+       u64 dawrx0;
  };

  static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
@@ -677,6 +679,10 @@ static unsigned long power9_idle_stop(unsigned long psscr, 
bool mmu_on)
                sprs.tscr       = mfspr(SPRN_TSCR);
                if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
                        sprs.ldbar = mfspr(SPRN_LDBAR);
+               if (cpu_has_feature(CPU_FTR_ARCH_31)) {
+                       sprs.dawr0 = mfspr(SPRN_DAWR0);
+                       sprs.dawrx0 = mfspr(SPRN_DAWRX0);
+               }

But this is within the if condition which says

        if ((psscr & PSSCR_RL_MASK) >= pnv_first_spr_loss_level)

This if condition is meant for stop4 and stop5 since these are stop
levels that have OPAL_PM_LOSE_HYP_CONTEXT set.

Since we can lose DAWR*, on states that lose limited hypervisor
context, such as stop0-2, we need to unconditionally save them
like AMR, IAMR etc.

Right, shallow states too loose DAWR/X. Thanks for pointing it out.
I'll fix this and resend.

                sprs_saved = true;

@@ -792,6 +798,10 @@ static unsigned long power9_idle_stop(unsigned long psscr, 
bool mmu_on)
        mtspr(SPRN_MMCR2,       sprs.mmcr2);
        if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
                mtspr(SPRN_LDBAR, sprs.ldbar);
+       if (cpu_has_feature(CPU_FTR_ARCH_31)) {
+               mtspr(SPRN_DAWR0, sprs.dawr0);
+               mtspr(SPRN_DAWRX0, sprs.dawrx0);
+       }

Likewise, we need to unconditionally restore these SPRs.

        mtspr(SPRN_SPRG3,       local_paca->sprg_vdso);

--
2.25.4

Thanks
Pratik