On Fri, Jul 17, 2020 at 10:38:23AM -0400, Athira Rajeev wrote:
> PowerISA v3.1 has few updates for the Branch History Rolling Buffer(BHRB).
>
> BHRB disable is controlled via Monitor Mode Control Register A (MMCRA)
> bit, namely "BHRB Recording Disable (BHRBRD)". This field controls
> whether BHRB entries are written when BHRB recording is enabled by other
> bits. This patch implements support for this BHRB disable bit.
>
> By setting 0b1 to this bit will disable the BHRB and by setting 0b0
> to this bit will have BHRB enabled. This addresses backward
> compatibility (for older OS), since this bit will be cleared and
> hardware will be writing to BHRB by default.
>
> This patch addresses changes to set MMCRA (BHRBRD) at boot for power10
> ( there by the core will run faster) and enable this feature only on
> runtime ie, on explicit need from user. Also save/restore MMCRA in the
> restore path of state-loss idle state to make sure we keep BHRB disabled
> if it was not enabled on request at runtime.
>
> Signed-off-by: Athira Rajeev <atraj...@linux.vnet.ibm.com>
For arch/powerpc/platforms/powernv/idle.c
Reviewed-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> ---
> arch/powerpc/perf/core-book3s.c | 20 ++++++++++++++++----
> arch/powerpc/perf/isa207-common.c | 12 ++++++++++++
> arch/powerpc/platforms/powernv/idle.c | 22 ++++++++++++++++++++--
> 3 files changed, 48 insertions(+), 6 deletions(-)
[..snip..]
> diff --git a/arch/powerpc/platforms/powernv/idle.c
> b/arch/powerpc/platforms/powernv/idle.c
> index 2dd4673..1c9d0a9 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -611,6 +611,7 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> unsigned long srr1;
> unsigned long pls;
> unsigned long mmcr0 = 0;
> + unsigned long mmcra = 0;
> struct p9_sprs sprs = {}; /* avoid false used-uninitialised */
> bool sprs_saved = false;
>
> @@ -657,6 +658,21 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> */
> mmcr0 = mfspr(SPRN_MMCR0);
> }
> +
> + if (cpu_has_feature(CPU_FTR_ARCH_31)) {
> + /*
> + * POWER10 uses MMCRA (BHRBRD) as BHRB disable bit.
> + * If the user hasn't asked for the BHRB to be
> + * written, the value of MMCRA[BHRBRD] is 1.
> + * On wakeup from stop, MMCRA[BHRBD] will be 0,
> + * since it is previleged resource and will be lost.
> + * Thus, if we do not save and restore the MMCRA[BHRBD],
> + * hardware will be needlessly writing to the BHRB
> + * in problem mode.
> + */
> + mmcra = mfspr(SPRN_MMCRA);
> + }
> +
> if ((psscr & PSSCR_RL_MASK) >= pnv_first_spr_loss_level) {
> sprs.lpcr = mfspr(SPRN_LPCR);
> sprs.hfscr = mfspr(SPRN_HFSCR);
> @@ -700,8 +716,6 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> WARN_ON_ONCE(mfmsr() & (MSR_IR|MSR_DR));
>
> if ((srr1 & SRR1_WAKESTATE) != SRR1_WS_NOLOSS) {
> - unsigned long mmcra;
> -
> /*
> * We don't need an isync after the mtsprs here because the
> * upcoming mtmsrd is execution synchronizing.
> @@ -721,6 +735,10 @@ static unsigned long power9_idle_stop(unsigned long
> psscr, bool mmu_on)
> mtspr(SPRN_MMCR0, mmcr0);
> }
>
> + /* Reload MMCRA to restore BHRB disable bit for POWER10 */
> + if (cpu_has_feature(CPU_FTR_ARCH_31))
> + mtspr(SPRN_MMCRA, mmcra);
> +
> /*
> * DD2.2 and earlier need to set then clear bit 60 in MMCRA
> * to ensure the PMU starts running.
> --
> 1.8.3.1
>
