Subject: [PATCH v8 14/21] ACPI / processor: Make it possible to get CPU hardware ID via GICC

From: [email-masked] (Will Deacon)
Date: Mon, 9 Feb 2015 06:55:12 +0000

On Mon, Feb 02, 2015 at 12:45:42PM +0000, Hanjun Guo wrote:
> Introduce a new function map_gicc_mpidr() to allow MPIDRs to be obtained
> from the GICC Structure introduced by ACPI 5.1.
> 
> MPIDR is the CPU hardware ID as local APIC ID on x86 platform, so we use
> MPIDR not the GIC CPU interface ID to identify CPUs.
> 
> Further steps would typedef a phys_id_t for in arch code(with
> appropriate size and a corresponding invalid value, say ~0) and use that
> instead of an int in drivers/acpi/processor_core.c to store phys_id, then
> no need for mpidr packing.
> 
> CC: Rafael J. Wysocki <[email-masked]>
> CC: Catalin Marinas <[email-masked]>
> CC: Will Deacon <[email-masked]>
> Tested-by: Suravee Suthikulpanit <[email-masked]>
> Tested-by: Yijing Wang <[email-masked]>
> Tested-by: Mark Langsdorf <[email-masked]>
> Tested-by: Jon Masters <[email-masked]>
> Tested-by: Timur Tabi <[email-masked]>
> Signed-off-by: Hanjun Guo <[email-masked]>
> ---
>  arch/arm64/include/asm/acpi.h | 30 ++++++++++++++++++++++++++++++
>  drivers/acpi/processor_core.c | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 67 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index 8984aa5..7e825b9 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -12,6 +12,8 @@
>  #ifndef _ASM_ACPI_H
>  #define _ASM_ACPI_H
>  
> +#include <asm/smp_plat.h>
> +
>  /* Basic configuration for ACPI */
>  #ifdef	CONFIG_ACPI
>  #define acpi_strict 1	/* No out-of-spec workarounds on ARM64 */
> @@ -45,6 +47,34 @@ static inline void enable_acpi(void)
>  	acpi_noirq = 0;
>  }
>  
> +/* MPIDR value provided in GICC structure is 64 bits, but the
> + * existing phys_id (CPU hardware ID) using in acpi processor
> + * driver is 32-bit, to conform to the same datatype we need
> + * to repack the GICC structure MPIDR.
> + *
> + * bits other than following 32 bits are defined as 0, so it
> + * will be no information lost after repacked.
> + *
> + * Bits [0:7] Aff0;
> + * Bits [8:15] Aff1;
> + * Bits [16:23] Aff2;
> + * Bits [32:39] Aff3;
> + */
> +static inline u32 pack_mpidr(u64 mpidr)
> +{
> +	return (u32) ((mpidr & 0xff00000000) >> 8) | mpidr;
> +}

I'm a bit puzzled by this packing:

  - Bit 31 of the MPIDR is RES1. Do we need to mask it out first?
  - How does this work for uniprocessor systems where bit 30 is set?
  - Similarly for mythical multi-threaded implementations with bit 24 set.

Will