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

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Message-ID: <20150209065512.GK13969@arm.com>
Date:	Mon, 9 Feb 2015 06:55:12 +0000
From:	Will Deacon <will.deacon@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Mark Rutland <Mark.Rutland@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Timur Tabi <timur@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Mark Langsdorf <mlangsdo@...hat.com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH v8 14/21] ACPI / processor: Make it possible to get CPU
 hardware ID via GICC

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 <rjw@...ysocki.net>
> CC: Catalin Marinas <catalin.marinas@....com>
> CC: Will Deacon <will.deacon@....com>
> Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> Tested-by: Yijing Wang <wangyijing@...wei.com>
> Tested-by: Mark Langsdorf <mlangsdo@...hat.com>
> Tested-by: Jon Masters <jcm@...hat.com>
> Tested-by: Timur Tabi <timur@...eaurora.org>
> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> ---
>  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
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