Re: [Linaro-acpi] [PATCH v3 10/17] ACPI / processor: Make it possible to get CPU hardware ID via GICC

Hi Hanjun,

On Mon, Sep 01, 2014 at 03:57:48PM +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@linaro.org

arch/arm64/include/asm/acpi.h | 32 ++++++++++++++++++++++++++++++++ arch/arm64/kernel/acpi.c | 1 - drivers/acpi/processor_core.c | 37 +++++++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h index e013dbb..a867467 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 */ @@ -38,6 +40,36 @@ static inline void disable_acpi(void) acpi_noirq = 1; } +/* MPIDR value provided in GICC structure is 64 bits, but

• • the acpi processor driver use the 32 bits cpu hardware
• • ID (apic_id on intel platform) everywhere, it is pretty
• • hard to modify the acpi processor driver to accept the
• • 64 bits MPIDR value, at the same time, only 32 bits of
• • the MPIDR is used in the 64 bits MPIDR, just pack the
• • Affx fields into a single 32 bit identifier to accommodate
• • the acpi processor drivers.
• */

I have comments on the code in this patch, but they are not the most important point. What I am really worried about, it is that as ARM, I do not want to know what an apic_id is. This code is *supposed* to be generic and yet it is chock-full of x86 specific stuff and you are trying to make ARM HW concepts fit with x86 ones, and I am not happy with that.

To be clearer, why does not this look-up of:

logical-cpu-index -> physical-cpu-index

is not carried out using the acpi_id ? Every architecture will have to add arch specific code to carry out the reverse look-up:

acpi_id -> apic_id (x86) acpi_id -> mpidr_el1 (arm64)

and the code would end up being split in a nice way. On top of that, I wonder why ACPI structures like eg struct acpi_processor contain x86 specific data (ie apic_id). I know it is a HW identifier as the MPIDR_EL1 is on arm64, but I do not want to deal with that in generic ACPI code because that's not generic at ALL.

What if another architecture wants to use ACPI ? Are we going to map its HW CPU identifier to an apic_id only because that's what x86 requires ?

I am sorry I do not like that. I understand it is easier to map ARM code to existing ACPI structures but I feel we will run into issues very soon because of that.

Is it that complex to remove the apic_id dependency in *generic* ACPI code and replace it with functions that hook into arch specific code to carry out the logical to physical cpu mappings ?

I understand this is harder to do, but it will make your life easier in the long run. I am thinking of other pieces of code like the supposedly generic ACPI CPUidle driver, where we *still* depend on the apic to detect idle states, this is not going to fly, I am sorry, we need to have code that has a chance to be generic from the beginning not as an afterthought.

Lorenzo

+static inline u32 pack_mpidr_into_32_bits(u64 mpidr) +{

• /*

• * Bits [0:7] Aff0;
  

• * Bits [8:15] Aff1;
  

• * Bits [16:23] Aff2;
  

• * Bits [32:39] Aff3;
  

• */
  

• 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_into_32_bits(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 fbaaf01..35dff11 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;
  

• return 0;
  

• }
• return -EINVAL;

+}

static int map_madt_entry(int type, u32 acpi_id) { unsigned long madt_end, entry; @@ -99,6 +131,9 @@ static int map_madt_entry(int type, u32 acpi_id) } else if (header->type == ACPI_MADT_TYPE_LOCAL_SAPIC) { if (!map_lsapic_id(header, type, acpi_id, &apic_id)) break;

• } else if (header->type == ACPI_MADT_TYPE_GENERIC_INTERRUPT) {
  

• 	if (!map_gicc_mpidr(header, type, acpi_id, &apic_id))
  

• 		break;
  

  } entry += header->length; }

@@ -131,6 +166,8 @@ static int map_mat_entry(acpi_handle handle, int type, u32 acpi_id) map_lsapic_id(header, type, acpi_id, &apic_id); } else if (header->type == ACPI_MADT_TYPE_LOCAL_X2APIC) { map_x2apic_id(header, type, acpi_id, &apic_id);

• } else if (header->type == ACPI_MADT_TYPE_GENERIC_INTERRUPT) {

• map_gicc_mpidr(header, type, acpi_id, &apic_id);
  

  }

exit: -- 1.7.9.5