Re: [PATCH v5 12/18] ACPI / processor: Make it possible to get CPU hardware ID via GICC

[Hanjun Guo]

On 2014-10-30 5:33, Rafael J. Wysocki wrote:
> On Monday, October 27, 2014 05:58:10 PM Hanjun Guo wrote:
>> On 2014-10-25 1:39, Lorenzo Pieralisi wrote:
>>> On Fri, Oct 17, 2014 at 02:37:08PM +0100, 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.
>>>>
>>>> Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
>>>> ---
>>>>  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..483ff45 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))
>>>> +
>>>>  /*
>>>>   * It's used from ACPI core in kdump to boot UP system with SMP kernel,
>>>>   * with this check the ACPI core will not override the CPU index
>>>> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
>>>> index 34837e0..e91ec76 100644
>>>> --- a/arch/arm64/kernel/acpi.c
>>>> +++ b/arch/arm64/kernel/acpi.c
>>>> @@ -24,7 +24,6 @@
>>>>  #include <linux/bootmem.h>
>>>>  #include <linux/smp.h>
>>>>  
>>>> -#include <asm/smp_plat.h>
>>>>  #include <asm/cputype.h>
>>>>  #include <asm/cpu_ops.h>
>>>>  
>>>> diff --git a/drivers/acpi/processor_core.c b/drivers/acpi/processor_core.c
>>>> index e32321c..4007313 100644
>>>> --- a/drivers/acpi/processor_core.c
>>>> +++ b/drivers/acpi/processor_core.c
>>>> @@ -64,6 +64,38 @@ static int map_lsapic_id(struct acpi_subtable_header *entry,
>>>>  	return 0;
>>>>  }
>>>>  
>>>> +/*
>>>> + * On ARM platform, MPIDR value is the hardware ID as apic ID
>>>> + * on Intel platforms
>>>> + */
>>>> +static int map_gicc_mpidr(struct acpi_subtable_header *entry,
>>>> +		int device_declaration, u32 acpi_id, int *mpidr)
>>>> +{
>>>> +	struct acpi_madt_generic_interrupt *gicc =
>>>> +	    container_of(entry, struct acpi_madt_generic_interrupt, header);
>>>> +
>>>> +	if (!(gicc->flags & ACPI_MADT_ENABLED))
>>>> +		return -ENODEV;
>>>> +
>>>> +	/* In the GIC interrupt model, logical processors are
>>>> +	 * required to have a Processor Device object in the DSDT,
>>>> +	 * so we should check device_declaration here
>>>> +	 */
>>>> +	if (device_declaration && (gicc->uid == acpi_id)) {
>>>> +		/*
>>>> +		 * Only bits [0:7] Aff0, bits [8:15] Aff1, bits [16:23] Aff2
>>>> +		 * and bits [32:39] Aff3 are meaningful, so pack the Affx
>>>> +		 * fields into a single 32 bit identifier to accommodate the
>>>> +		 * acpi processor drivers.
>>>> +		 */
>>>> +		*mpidr = ((gicc->arm_mpidr & 0xff00000000) >> 8)
>>>> +			 | gicc->arm_mpidr;
>>>
>>> The simple fact that you define a function to pack the mpidr value and
>>> you can't use it here because this is *generic* code is telling, and
>>> a very bad omen. At the cost of sounding like a broken record, I do not
>>> like this mpidr->apic->logical_cpu song and dance at all.
>>> ACPI is peppered with code (eg hotplug is another example, CPUidle driver
>>> even worse) that is supposed to be generic but contains x86 code to carry
>>> out this cpuid conversion, I really think that in order to start an ARM64
>>> ACPI port properly we should at least try to factor out this physical to
>>> logical cpu id conversion, and it is not the first time that I mention this
>>> on the lists.
>>
>> I know, thanks for pointing this out. As I replied in previous version
>> of this patch set, apic_id is x86/ia64 specific, but the meaning behind
>> it is not. It means the CPU hardware id to identify itself in the system,
>> it just like MPIDR on ARM.
>>
>> I will send out a patch for RFC to convert apic_id to physid which
>> is generic for all platforms.
>>
>>>
>>> I will also talk to Rafael about this at the earliest opportunity, I
>>> guess that x86 code relies on apic-id because some ACPI versions could
>>> not rely on the acpi-id or some other reasons I have to investigate.
>>
>> As ACPI spec (section 8.4, Declaring Processors) said, Each processor
>> in the system must be declared in the ACPI namespace, so each cpu will
>> have acpi_id in all ACPI versions, and in theory we can map acpi_id to
>> logical cpu id if we want to.
>>
>> But things are complicated, apic_id is connected to many
>> tables, MADT for smp init, DSDT for device driver, and SRAT for NUMA (there
>> is no acpi_id in it, ONLY has apic_id in the table for x86/ia64), so if we
>> want to factor the code to map acpi_id to logical cpu id, we need to modify:
>>
>>  - ACPI drivers;
>>  - SMP init for x86 and ia64
>>  - the mappings for NUMA init for x86 and ia64
>> that will be lots of work I think.
> 
> And error prone for that matter.

Thanks for the clarify, I will send out a patch set to convert apic_id to
phys_id in ACPI processor driver soon, then we don't need to map acpi_id
to logical cpu number.

Thanks
Hanjun
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