Re: [PATCH v3 2/5] ACPI/PPTT: Add function to return ACPI 6.3 Identical tokens

[Sudeep Holla <sudeep.holla@arm.com>]

On Fri, May 03, 2019 at 06:24:04PM -0500, Jeremy Linton wrote:
> ACPI 6.3 adds a flag to indicate that child nodes are all
> identical cores. This is useful to authoritatively determine
> if a set of (possibly offline) cores are identical or not.
> 
> Since the flag doesn't give us a unique id we can generate
> one and use it to create bitmaps of sibling nodes, or simply
> in a loop to determine if a subset of cores are identical.
>

If possible reorder this patch with next just to be sure.
I know the user is not introduced until 4/5, but 3/5 kind of fixes
the implementation.


Apart from that, this looks fine to me.

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  drivers/acpi/pptt.c  | 26 ++++++++++++++++++++++++++
>  include/linux/acpi.h |  5 +++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 83a026765faa..1865515297ca 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -660,3 +660,29 @@ int find_acpi_cpu_topology_package(unsigned int cpu)
>  	return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
>  					  ACPI_PPTT_PHYSICAL_PACKAGE);
>  }
> +
> +/**
> + * find_acpi_cpu_topology_hetero_id() - Get a core architecture tag
> + * @cpu: Kernel logical CPU number
> + *
> + * Determine a unique heterogeneous tag for the given CPU. CPUs with the same
> + * implementation should have matching tags.
> + *
> + * The returned tag can be used to group peers with identical implementation.
> + *
> + * The search terminates when a level is found with the identical implementation
> + * flag set or we reach a root node.
> + *
> + * Due to limitations in the PPTT data structure, there may be rare situations
> + * where two cores in a heterogeneous machine may be identical, but won't have
> + * the same tag.
> + *

Indeed, it's unfortunate. I gave some thoughts if we can find ways to
avoid this. Hope we don't have to see such weird combinations with ACPI
based systems.

--
Regards,
Sudeep