Re: [Qemu-devel] [PATCH RFC V2 1/4] Use Aff1 with mpidr

[Igor Mammedov <imammedo@redhat.com>]

On Wed,  6 May 2015 17:04:39 +0300
shlomopongratz@gmail.com wrote:

> From: Shlomo Pongratz <shlomo.pongratz@huawei.com>
> 
> In order to support up to 128 cores with GIC-500 (GICv3 implementation)
> affinity1 must be used. GIC-500 support up to 32 clusters with up to
> 8 cores in a cluster. So for example, if one wishes to have 16 cores,
> the options are: 2 clusters of 8 cores each, 4 clusters with 4 cores each
> Currently only the first option is supported.
> In order to have more flexible scheme the virt machine must pass the
> desired scheme.
> 
> Signed-off-by: Shlomo Pongratz <shlomo.pongratz@huawei.com>
> ---
>  target-arm/helper.c | 12 ++++++++++--
>  target-arm/psci.c   | 18 ++++++++++++++++--
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index f8f8d76..f555c0b 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -2035,11 +2035,19 @@ static const ARMCPRegInfo strongarm_cp_reginfo[] = {
>  static uint64_t mpidr_read(CPUARMState *env, const ARMCPRegInfo *ri)
>  {
>      CPUState *cs = CPU(arm_env_get_cpu(env));
> -    uint32_t mpidr = cs->cpu_index;
> -    /* We don't support setting cluster ID ([8..11]) (known as Aff1
> +    uint32_t mpidr, aff0, aff1;
> +    uint32_t cpuid = cs->cpu_index;
> +    /* We don't support setting cluster ID ([16..23]) (known as Aff2
>       * in later ARM ARM versions), or any of the higher affinity level fields,
>       * so these bits always RAZ.
>       */
> +    /* Currently GIC-500 code supports 64 cores in 16 clusters with 8 cores each
> +     * Future code will remove this limitation.
> +     * This code is valid for GIC-400 too.
> +     */
> +    aff0 = cpuid % 8;
Even though GIC-500 spec says that it supports 8 cores I haven't found
in it how it encodes aff0 but encoding is specified by respective
CPU specs. I've checked a53, a57, a72 specs and they limit aff0
to max 0x3 value.
I think encoding should be CPU type specific i.e. not defined by what
GIC can support and once we add CPU type with 8 cores, it would provide
it's own version of mpidr_read since it would be defined by spec
how to encode aff0.

> +    aff1 = cpuid / 8;
> +    mpidr = (aff1 << 8) | aff0;
>      if (arm_feature(env, ARM_FEATURE_V7MP)) {
>          mpidr |= (1U << 31);
>          /* Cores which are uniprocessor (non-coherent)
> diff --git a/target-arm/psci.c b/target-arm/psci.c
> index d8fafab..64fbe61 100644
> --- a/target-arm/psci.c
> +++ b/target-arm/psci.c
> @@ -86,6 +86,7 @@ void arm_handle_psci_call(ARMCPU *cpu)
>      CPUARMState *env = &cpu->env;
>      uint64_t param[4];
>      uint64_t context_id, mpidr;
> +    uint32_t core, Aff1, Aff0;
>      target_ulong entry;
>      int32_t ret = 0;
>      int i;
> @@ -121,7 +122,16 @@ void arm_handle_psci_call(ARMCPU *cpu)
>  
>          switch (param[2]) {
>          case 0:
> -            target_cpu_state = qemu_get_cpu(mpidr & 0xff);
> +            /* MPIDR_EL1 [RES0:affinity-3:RES1:U:RES0:MT:affinity-1:affinity-0]
> +             * GIC 500 code currently supports 32 clusters with 8 cores each
> +             * but no more than 128 cores. Future version will have flexible
> +             * affinity selection
> +             * GIC 400 supports 8 cores so 0x7 for Aff0 is O.K. too
> +             */
> +            Aff1 = (mpidr & 0xff00) >> (8 - 3); /* Shift by 8 multiply by 8 */
> +            Aff0 = mpidr & 0x7;
> +            core = Aff1 + Aff0;
> +            target_cpu_state = qemu_get_cpu(core);
>              if (!target_cpu_state) {
>                  ret = QEMU_PSCI_RET_INVALID_PARAMS;
>                  break;
> @@ -153,7 +163,11 @@ void arm_handle_psci_call(ARMCPU *cpu)
>          context_id = param[3];
>  
>          /* change to the cpu we are powering up */
> -        target_cpu_state = qemu_get_cpu(mpidr & 0xff);
> +        /* Currently supports 64 cores in 16 clusters with 8 cores each */
> +        Aff1 = (mpidr & 0xff00) >> (8 - 3); /* Shift by 8 multiply by 8 */
> +        Aff0 = mpidr & 0x7;
> +        core = Aff1 + Aff0;
> +        target_cpu_state = qemu_get_cpu(core);
>          if (!target_cpu_state) {
>              ret = QEMU_PSCI_RET_INVALID_PARAMS;
>              break;