Re: [PATCH v4 2/3] xen/arm: Check for PMU platform support

[Julien Grall <julien@xxxxxxx>]

Hi Michal,

On 11/10/2021 10:00, Michal Orzel wrote:
> ID_AA64DFR0_EL1/ID_DFR0_EL1 registers provide
> information about PMU support. Replace structure
> dbg64/dbg32 with a union and fill in all the
> register fields according to document:
> ARM Architecture Registers(DDI 0595, 2021-06).
>
> Add macros boot_dbg_feature64/boot_dbg_feature32
> to check for a debug feature. Add macro
> cpu_has_pmu to check for PMU support.
>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> ---
> Changes since v3:
> -none
> Changes since v2:
> -none
> Changes since v1:
> -new in v2
> ---
>   xen/include/asm-arm/cpufeature.h | 49 ++++++++++++++++++++++++++++++--
>   1 file changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
> index 5ca09b0bff..4fce23844d 100644
> --- a/xen/include/asm-arm/cpufeature.h
> +++ b/xen/include/asm-arm/cpufeature.h
> @@ -4,6 +4,7 @@
>   #ifdef CONFIG_ARM_64
>   #define cpu_feature64(c, feat)         ((c)->pfr64.feat)
>   #define boot_cpu_feature64(feat)       (system_cpuinfo.pfr64.feat)
> +#define boot_dbg_feature64(feat)       (system_cpuinfo.dbg64.feat)
>   
>   #define cpu_feature64_has_el0_32(c)    (cpu_feature64(c, el0) == 2)
>   
> @@ -22,6 +23,7 @@
>   
>   #define cpu_feature32(c, feat)         ((c)->pfr32.feat)
>   #define boot_cpu_feature32(feat)       (system_cpuinfo.pfr32.feat)
> +#define boot_dbg_feature32(feat)       (system_cpuinfo.dbg32.feat)
>   
>   #define cpu_has_arm       (boot_cpu_feature32(arm) == 1)
>   #define cpu_has_thumb     (boot_cpu_feature32(thumb) >= 1)
> @@ -32,8 +34,10 @@
>   
>   #ifdef CONFIG_ARM_32
>   #define cpu_has_gentimer  (boot_cpu_feature32(gentimer) == 1)
> +#define cpu_has_pmu       (boot_dbg_feature32(perfmon) >= 1)
From my understanding, on Armv7, perfmon == 0 only means PMUv2 is not 
present. IOW, it doesn't say whether PMUv1 is supported.
I think it is OK to treat as the PMU is not supported (ARMv8 treat it 
like that too), but I would like a comment in the code so it is clear 
this is a deliberate choice.
>   #else
>   #define cpu_has_gentimer  (1)
> +#define cpu_has_pmu       (boot_dbg_feature64(pmu_ver) >= 1)
>   #endif
>   #define cpu_has_security  (boot_cpu_feature32(security) > 0)
>   
> @@ -181,8 +185,28 @@ struct cpuinfo_arm {
>           };
>       } pfr64;
>   
> -    struct {
> +    union {
>           register_t bits[2];
> +        struct {
> +            /* DFR0 */
> +            unsigned long debug_ver:4;
> +            unsigned long trace_ver:4;
> +            unsigned long pmu_ver:4;
> +            unsigned long brps:4;
> +            unsigned long __res0:4;
> +            unsigned long wrps:4;
> +            unsigned long __res1:4;
> +            unsigned long ctx_cmps:4;
> +            unsigned long pms_ver:4;
> +            unsigned long double_lock:4;
> +            unsigned long trace_filt:4;
> +            unsigned long __res2:4;
> +            unsigned long mtpmu:4;
> +            unsigned long __res3:12;
> +
> +            /* DFR1 */
> +            unsigned long __res4:64;
> +        };
>       } dbg64;
>   
>       struct {
> @@ -321,8 +345,29 @@ struct cpuinfo_arm {
>           };
>       } pfr32;
>   
> -    struct {
> +    union {
>           register_t bits[2];
> +        struct {
> +            /* DFR0 */
> +            unsigned long copdbg:4;
> +            unsigned long copsdbg:4;
> +            unsigned long mmapdbg:4;
> +            unsigned long coptrc:4;
> +            unsigned long mmaptrc:4;
> +            unsigned long mprofdbg:4;
> +            unsigned long perfmon:4;
> +            unsigned long tracefilt:4;
> +#ifdef CONFIG_ARM_64
> +            unsigned long __res0:32;
> +#endif
> +
> +            /* DFR1 */
> +            unsigned long mtpmu:4;
> +            unsigned long __res1:28;
> +#ifdef CONFIG_ARM_64
> +            unsigned long __res2:32;
> +#endif
> +        };
>       } dbg32;
>   
>       struct {
Cheers,

--
Julien Grall