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Cc:     Sudeep Holla <sudeep.holla@arm.com>, ard.biesheuvel@linaro.org,
        shunyong.yang@hxt-semitech.com, yu.zheng@hxt-semitech.com,
        catalin.marinas@arm.com, will.deacon@arm.com
Subject: Re: [PATCH] arm64: acpi: reenumerate topology ids
To:     Andrew Jones <drjones@redhat.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        jeremy.linton@arm.com
References: <20180628145128.10057-1-drjones@redhat.com>
From:   Sudeep Holla <sudeep.holla@arm.com>
Organization: ARM
Message-ID: <a38fb684-c023-1a96-464e-dd268f3132ea@arm.com>
Date:   Thu, 28 Jun 2018 17:30:51 +0100
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On 28/06/18 15:51, Andrew Jones wrote:
> When booting with devicetree, and the devicetree has the cpu-map
> node, the topology IDs that are visible from sysfs are generated
> with counters. ACPI, on the other hand, uses ACPI table pointer
> offsets, which, while guaranteed to be unique, look a bit weird.
> Instead, we can generate DT identical topology IDs for ACPI by
> just using counters for the leaf nodes and by remapping the
> non-leaf table pointer offsets to counters.
> 
> Cc: Jeremy Linton <jeremy.linton@arm.com>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
> 
> v1:
> Reworked this since the RFC in order to make the algorithm more
> obvious. It wasn't clear in the RFC that the ACPI nodes could be
> in any order, although they could have been. I've tested that
> this works with nodes in arbitrary order by hacking the QEMU
> PPTT table generator[*].
> 
> Note, while this produces equivalent topology IDs to what the
> DT cpu-map node produces for all sane configs, if PEs are
> threads (have MPIDR.MT set), but the cpu-map does not specify
> threads, then, while the DT parsing code will happily call the
> threads "cores", ACPI will see that the PPTT leaf nodes are for
> threads and produce different topology IDs. I see this difference
> as a bug with the DT parsing which can be addressed separately.
> 
> [*] https://github.com/rhdrjones/qemu/commits/virt-cpu-topology
> 
> 
>  arch/arm64/kernel/topology.c | 70 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 55 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index f845a8617812..7ef457401b24 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -316,6 +316,10 @@ static void __init reset_cpu_topology(void)
>  }
>  
>  #ifdef CONFIG_ACPI
> +
> +#define acpi_topology_mktag(x)	(-((x) + 1))
> +#define acpi_topology_istag(x)	((x) < 0)
> +
>  /*
>   * Propagate the topology information of the processor_topology_node tree to the
>   * cpu_topology array.
> @@ -323,27 +327,31 @@ static void __init reset_cpu_topology(void)
>  static int __init parse_acpi_topology(void)
>  {
>  	bool is_threaded;
> -	int cpu, topology_id;
> +	int package_id = 0;
> +	int cpu, ret;
>  
>  	is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
>  
> +	/*
> +	 * Loop through all PEs twice. In the first loop store parent
> +	 * tags into the IDs. In the second loop we reset the IDs as
> +	 * 0..N-1 per parent tag.
> +	 */
> +
>  	for_each_possible_cpu(cpu) {
>  		int i, cache_id;
>  
> -		topology_id = find_acpi_cpu_topology(cpu, 0);
> -		if (topology_id < 0)
> -			return topology_id;
> -
> -		if (is_threaded) {
> -			cpu_topology[cpu].thread_id = topology_id;
> -			topology_id = find_acpi_cpu_topology(cpu, 1);
> -			cpu_topology[cpu].core_id   = topology_id;
> -		} else {
> -			cpu_topology[cpu].thread_id  = -1;
> -			cpu_topology[cpu].core_id    = topology_id;
> -		}
> -		topology_id = find_acpi_cpu_topology_package(cpu);
> -		cpu_topology[cpu].package_id = topology_id;
> +		ret = find_acpi_cpu_topology(cpu, 0);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (is_threaded)
> +			ret = find_acpi_cpu_topology(cpu, 1);
> +		else
> +			cpu_topology[cpu].thread_id = -1;
> +		cpu_topology[cpu].core_id = acpi_topology_mktag(ret);
> +		ret = find_acpi_cpu_topology_package(cpu);
> +		cpu_topology[cpu].package_id = acpi_topology_mktag(ret);

I am not sure if we can ever guarantee that DT and ACPI will get the
same ids whatever counter we use as it depends on the order presented in
the firmware(DT or ACPI). So I am not for generating ids for core and
threads in that way.

So I would like to keep it simple and just have this counters for
package ids as demonstrated in Shunyong's patch.


Also looking @ topology_get_acpi_cpu_tag again now, we should have
valid flag check instead of level = 0. Jeremy ?

-- 
Regards,
Sudeep

diff --git i/drivers/acpi/pptt.c w/drivers/acpi/pptt.c
index e5ea1974d1e3..795c43053570 100644
--- i/drivers/acpi/pptt.c
+++ w/drivers/acpi/pptt.c
@@ -481,8 +481,12 @@ static int topology_get_acpi_cpu_tag(struct
acpi_table_header *table,
        if (cpu_node) {
                cpu_node = acpi_find_processor_package_id(table, cpu_node,
                                                          level, flag);
-               /* Only the first level has a guaranteed id */
-               if (level == 0)
+               /*
+                * As per specification if the processor structure
represents
+                * an actual processor ACPI processor ID must be valid,
which
+                * should be always true for level 0
+                */
+               if (cpu_node-flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID)
                        return cpu_node->acpi_processor_id;
                return ACPI_PTR_DIFF(cpu_node, table);
        }