linux-kernel - Re: [PATCH v5 3/5] ACPI / processor: Introduce map_gic_id() to get apic id from MADT or

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Date:	Wed, 19 Feb 2014 14:33:40 +0000
From:	Sudeep Holla <Sudeep.Holla@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Sudeep.Holla@....com, Lan Tianyu <tianyu.lan@...el.com>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Joe Perches <joe@...ches.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 3/5] ACPI / processor: Introduce map_gic_id() to get
 apic id from MADT or _MAT method

Hi Hanjun,

On 18/02/14 16:23, Hanjun Guo wrote:
> Get apic id from MADT or _MAT method is not implemented on arm/arm64,
> and ACPI 5.0 introduces GIC Structure for it, so this patch introduces
> map_gic_id() to get apic id followed the ACPI 5.0 spec.
> 
> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> ---
>  drivers/acpi/processor_core.c |   26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/acpi/processor_core.c b/drivers/acpi/processor_core.c
> index 4dcf776..d316d9b 100644
> --- a/drivers/acpi/processor_core.c
> +++ b/drivers/acpi/processor_core.c
> @@ -71,6 +71,27 @@ static int map_lsapic_id(struct acpi_subtable_header *entry,
>  	return 0;
>  }
>  
> +static int map_gic_id(struct acpi_subtable_header *entry,
> +		int device_declaration, u32 acpi_id, int *apic_id)
> +{
> +	struct acpi_madt_generic_interrupt *gic =
> +		(struct acpi_madt_generic_interrupt *)entry;
> +
> +	if (!(gic->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 && (gic->uid == acpi_id)) {
> +		*apic_id = gic->gic_id;

I have mentioned this earlier, it's not clear yet to me how does this work ?
It needs more clarity in the form of comment here at-least as the ACPIv5.0 is
also not so clear or explicit on how to handle this.

Here you are expecting gic->uid = acpi_id which is fine, while acpi_map_cpuid
matches apic_id with cpu_physical_id(which must be MPIDR in ARM{32,64}). The
latter imposes restriction that gic->gic_id has to be MPIDR. Does that mean we
are imposing restriction on GIC ID to be MPIDR ? If so please document it here
and please explain the reason behind that choice.

I would expect _UID to be MPIDR rather than GIC ID but you may have some reasons
for this choice.

Regards,
Sudeep

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