Re: [PATCH 3/8] arm64: pmu: Add support for probing with ACPI

[Will Deacon <will.deacon@arm.com>]

On Thu, Jun 09, 2016 at 05:23:28PM -0500, Jeremy Linton wrote:
> From: Mark Salter <msalter@redhat.com>
> 
> In the case of ACPI, the PMU IRQ information is contained in the
> MADT table. Also, since the PMU does not exist as a device in the
> ACPI DSDT table, it is necessary to create a platform device so
> that the appropriate driver probing is triggered.
> 
> Signed-off-by: Mark Salter <msalter@redhat.com>
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
> 
>  NOTE: Much of the code in pmu_acpi_init() is replaced in a later version
>        of this patch. The later version of the patch cleans up some of the
>        possible style/error handling issues that have been pointed out with
>        this version.
> 
>  arch/arm64/kernel/smp.c      |  5 +++
>  drivers/perf/Kconfig         |  4 ++
>  drivers/perf/Makefile        |  1 +
>  drivers/perf/arm_pmu_acpi.c  | 97 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/perf/arm_pmu.h |  7 ++++
>  5 files changed, 114 insertions(+)
>  create mode 100644 drivers/perf/arm_pmu_acpi.c
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 678e084..5c96d23 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -37,6 +37,7 @@
>  #include <linux/completion.h>
>  #include <linux/of.h>
>  #include <linux/irq_work.h>
> +#include <linux/perf/arm_pmu.h>
>  
>  #include <asm/alternative.h>
>  #include <asm/atomic.h>
> @@ -540,6 +541,7 @@ acpi_map_gic_cpu_interface(struct acpi_madt_generic_interrupt *processor)
>  			return;
>  		}
>  		bootcpu_valid = true;
> +		arm_pmu_parse_acpi(0, processor);
>  		return;
>  	}
>  
> @@ -560,6 +562,9 @@ acpi_map_gic_cpu_interface(struct acpi_madt_generic_interrupt *processor)
>  	 */
>  	acpi_set_mailbox_entry(cpu_count, processor);
>  
> +	/* get PMU irq info */
> +	arm_pmu_parse_acpi(cpu_count, processor);
> +

Nit: the outer functions are now misnomers, since this has nothing to do
with the GIC. It feels like acpi_parse_gic_cpu_interface could use some
slight restructuring so that the MADT parsing looks less confused.

> diff --git a/drivers/perf/Makefile b/drivers/perf/Makefile
> index acd2397..fd8090d 100644
> --- a/drivers/perf/Makefile
> +++ b/drivers/perf/Makefile
> @@ -1 +1,2 @@
>  obj-$(CONFIG_ARM_PMU) += arm_pmu.o
> +obj-$(CONFIG_ARM_PMU_ACPI) += arm_pmu_acpi.o
> diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
> new file mode 100644
> index 0000000..98c452d
> --- /dev/null
> +++ b/drivers/perf/arm_pmu_acpi.c
> @@ -0,0 +1,97 @@
> +/*
> + * PMU support
> + *
> + * Copyright (C) 2015 Red Hat Inc.
> + * Author: Mark Salter <msalter@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include <linux/perf/arm_pmu.h>
> +#include <linux/platform_device.h>
> +#include <linux/acpi.h>
> +#include <linux/irq.h>
> +#include <linux/irqdesc.h>
> +
> +#define PMU_PDEV_NAME "armv8-pmu"

Stick this in include/linux/perf/arm_pmu.h where we can use it in the driver
code too?

> +
> +struct pmu_irq {
> +	int gsi;
> +	int trigger;
> +};
> +
> +static struct pmu_irq pmu_irqs[NR_CPUS] __initdata;
> +
> +void __init arm_pmu_parse_acpi(int cpu, struct acpi_madt_generic_interrupt *gic)
> +{
> +	pmu_irqs[cpu].gsi = gic->performance_interrupt;
> +	if (gic->flags & ACPI_MADT_PERFORMANCE_IRQ_MODE)
> +		pmu_irqs[cpu].trigger = ACPI_EDGE_SENSITIVE;
> +	else
> +		pmu_irqs[cpu].trigger = ACPI_LEVEL_SENSITIVE;
> +}
> +
> +static int __init pmu_acpi_init(void)
> +{
> +	struct platform_device *pdev;
> +	struct pmu_irq *pirq = pmu_irqs;
> +	struct resource	*res, *r;
> +	int err = -ENOMEM;
> +	int i, count, irq;
> +
> +	if (acpi_disabled)
> +		return 0;
> +
> +	/* Must have irq for boot boot cpu, at least */

boot boot

> +	if (pirq->gsi == 0)
> +		return -EINVAL;
> +
> +	irq = acpi_register_gsi(NULL, pirq->gsi, pirq->trigger,
> +				ACPI_ACTIVE_HIGH);

This is quite tricky to read, thanks to the aliasing of pirq and
pmu_irqs[0]. Why is it necessary to register the first gsi separately,
rather than just register it later in the loop with all the other
interrupts?

Will