Re: [PATCH v7 11/17] ACPI / processor: Make it possible to get CPU hardware ID via GICC

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Wed, Jan 14, 2015 at 03:04:59PM +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.
> 
> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> Tested-by: Yijing Wang <wangyijing@huawei.com>
> Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
> ---
>  arch/arm64/include/asm/acpi.h | 29 +++++++++++++++++++++++++++++
>  arch/arm64/kernel/acpi.c      |  1 -
>  drivers/acpi/processor_core.c | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index c82d4a1..639bb2a 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 +47,33 @@ static inline void enable_acpi(void)
>  	acpi_noirq = 0;
>  }
>  
> +/* MPIDR value provided in GICC structure is 64 bits, but the
> + * existing apic_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.
> + *
> + * Only 32 bits of MPIDR are used:
> + *
> + * 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;
> +}
> +
> +/*
> + * The ACPI processor driver for ACPI core code needs this macro
> + * to find out this cpu was already mapped (mapping from CPU hardware
> + * ID to CPU logical ID) or not.
> + *
> + * cpu_logical_map(cpu) is the mapping of MPIDR and the logical cpu,
> + * and MPIDR is the cpu hardware ID we needed to pack.
> + */
> +#define cpu_physical_id(cpu) pack_mpidr(cpu_logical_map(cpu))

Do we need this mpidr packing only because in drivers/acpi/processor_core.c
phys_id is defined as an int ?

What you could do, is to typedef a cpuid_t type 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.

phys_id is used as an error value too (ie -1 as a magic number), see
drivers/acpi/acpi_processor.c, retrieved through acpi_get_phys_id(),
it should not be that difficult to change the parsing API to keep current
code behaviour unchanged and define at the same time a proper type for
the cpu physical identifier, with no mpidr packing needed whatsoever.

Thanks,
Lorenzo