Re: [RFC PATCH 1/2] powerpc: Add a CPU feature bit for TM bug workarounds on POWER9 DD2.2

[Benjamin Herrenschmidt <benh@au1.ibm.com>]

On Fri, 2017-12-08 at 17:09 +1100, Paul Mackerras wrote:
> This adds a CPU feature bit which is set for POWER9 DD2.2 processors
> which will be used to enable software emulation for some transactional
> memory instructions, in order to work around hardware bugs.

The worry here is backward compatibility as we don't know yet which
processor will fix it (if ever).

Paul and Nick, can you also add it to the "new" CPU features mechanism
(which we should enable now) so that we at least have a way to control
this from firmware ?

> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> ---
>  arch/powerpc/include/asm/cputable.h |  5 ++++-
>  arch/powerpc/kernel/cputable.c      | 20 ++++++++++++++++++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
> index 53b31c2bcdf4..70cee46c046c 100644
> --- a/arch/powerpc/include/asm/cputable.h
> +++ b/arch/powerpc/include/asm/cputable.h
> @@ -215,6 +215,7 @@ enum {
>  #define CPU_FTR_DAWR			LONG_ASM_CONST(0x0400000000000000)
>  #define CPU_FTR_DABRX			LONG_ASM_CONST(0x0800000000000000)
>  #define CPU_FTR_PMAO_BUG		LONG_ASM_CONST(0x1000000000000000)
> +#define CPU_FTR_P9_TM_EMUL		LONG_ASM_CONST(0x2000000000000000)
>  #define CPU_FTR_POWER9_DD1		LONG_ASM_CONST(0x4000000000000000)
>  
>  #ifndef __ASSEMBLY__
> @@ -478,6 +479,7 @@ enum {
>  	    CPU_FTR_ARCH_207S | CPU_FTR_TM_COMP | CPU_FTR_ARCH_300)
>  #define CPU_FTRS_POWER9_DD1 ((CPU_FTRS_POWER9 | CPU_FTR_POWER9_DD1) & \
>  			     (~CPU_FTR_SAO))
> +#define CPU_FTRS_POWER9_DD2_2 (CPU_FTRS_POWER9 | CPU_FTR_P9_TM_EMUL)
>  #define CPU_FTRS_CELL	(CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
>  	    CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
>  	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
> @@ -496,7 +498,8 @@ enum {
>  	    (CPU_FTRS_POWER4 | CPU_FTRS_PPC970 | CPU_FTRS_POWER5 | \
>  	     CPU_FTRS_POWER6 | CPU_FTRS_POWER7 | CPU_FTRS_POWER8E | \
>  	     CPU_FTRS_POWER8 | CPU_FTRS_POWER8_DD1 | CPU_FTRS_CELL | \
> -	     CPU_FTRS_PA6T | CPU_FTR_VSX | CPU_FTRS_POWER9 | CPU_FTRS_POWER9_DD1)
> +	     CPU_FTRS_PA6T | CPU_FTR_VSX | CPU_FTRS_POWER9 | \
> +	     CPU_FTRS_POWER9_DD1 | CPU_FTRS_POWER9_DD2_2)
>  #endif
>  #else
>  enum {
> diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> index 760872916013..bb94bb6d9e4d 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -547,6 +547,26 @@ static struct cpu_spec __initdata cpu_specs[] = {
>  		.machine_check_early	= __machine_check_early_realmode_p9,
>  		.platform		= "power9",
>  	},
> +	{	/* Power9 DD2.2 */
> +		.pvr_mask		= 0xffffffff,
> +		.pvr_value		= 0x004e1202,
> +		.cpu_name		= "POWER9 (raw)",
> +		.cpu_features		= CPU_FTRS_POWER9_DD2_2,
> +		.cpu_user_features	= COMMON_USER_POWER9,
> +		.cpu_user_features2	= COMMON_USER2_POWER9,
> +		.mmu_features		= MMU_FTRS_POWER9,
> +		.icache_bsize		= 128,
> +		.dcache_bsize		= 128,
> +		.num_pmcs		= 6,
> +		.pmc_type		= PPC_PMC_IBM,
> +		.oprofile_cpu_type	= "ppc64/power9",
> +		.oprofile_type		= PPC_OPROFILE_INVALID,
> +		.cpu_setup		= __setup_cpu_power9,
> +		.cpu_restore		= __restore_cpu_power9,
> +		.flush_tlb		= __flush_tlb_power9,
> +		.machine_check_early	= __machine_check_early_realmode_p9,
> +		.platform		= "power9",
> +	},
>  	{	/* Power9 */
>  		.pvr_mask		= 0xffff0000,
>  		.pvr_value		= 0x004e0000,