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Date: Wed, 3 Sep 2014 17:27:39 +0100
From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To: Hanjun Guo <hanjun.guo@...aro.org>
Cc: Catalin Marinas <Catalin.Marinas@....com>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Mark Rutland <Mark.Rutland@....com>,
Olof Johansson <olof@...om.net>,
"grant.likely@...aro.org" <grant.likely@...aro.org>,
"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
Sudeep Holla <Sudeep.Holla@....com>,
Will Deacon <Will.Deacon@....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>,
Lv Zheng <lv.zheng@...el.com>,
Robert Moore <robert.moore@...el.com>,
Liviu Dudau <Liviu.Dudau@....com>,
Randy Dunlap <rdunlap@...radead.org>,
Charles Garcia-Tobin <Charles.Garcia-Tobin@....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 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@...aro.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
>
>
--
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