Re: [PATCH v7 2/7] x86/hygon: Map CPU NodeIds to DF nodes

[Yazen Ghannam]

On Fri, Oct 09, 2026 at 05:01:06PM +0800, Lin Wang wrote:
> On bare-metal Hygon systems, CPUID 0x8000001E ECX[7:0] encodes a
> CPU's socket and local CDD ordinal. The value is sparse across sockets
> and cannot directly index the dense DF node cache.
> 
> Resolve the encoded socket and local ordinal against CDD entries in the
> cache, which are ordered by socket and DFID. The NodeId reported by
> CPUID in a guest may not describe the physical DF topology, so return
> -ENODEV in guests or when it does not identify an enumerated CDD.
> 
> Hygon EDAC and ATL support will use this mapping. Keep it local until
> that support is added.
> 
> Signed-off-by: Lin Wang <wanglin@xxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/hygon_node.c | 55 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/arch/x86/kernel/hygon_node.c b/arch/x86/kernel/hygon_node.c
> index b83b1c8c40ea..4d492513a433 100644
> --- a/arch/x86/kernel/hygon_node.c
> +++ b/arch/x86/kernel/hygon_node.c
> @@ -17,6 +17,7 @@
>  
>  #include <linux/bitfield.h>
>  #include <linux/bitops.h>
> +#include <linux/cpufeature.h>
>  #include <linux/export.h>
>  #include <linux/init.h>
>  #include <linux/pci.h>
> @@ -24,6 +25,7 @@
>  #include <linux/processor.h>
>  #include <linux/slab.h>
>  #include <linux/sort.h>
> +#include <linux/topology.h>
>  
>  #include <asm/cpu_device_id.h>
>  #include <asm/hygon/node.h>
> @@ -481,6 +483,44 @@ static int __init sort_and_classify(struct df_node_cache *cache)
>  	return 0;
>  }
>  
> +#define NODE_ID_SOCKET	GENMASK(7, 4)
> +#define NODE_ID_LOCAL	GENMASK(3, 0)
> +
> +/*
> + * Translate a Hygon Fam18h phys_node_id (CPUID 8000001E ECX[7:0]) to a
> + * dense DF CDD index. On supported models, CPUID reports this
> + * encoding:
> + *
> + *   phys_node_id = (socket_id << 4) | local_cdd_index_in_dfid_order
> + *
> + * The CDD region of df_cache.nodes[] is sorted by (socket_id, dfid), so
> + * return the index of the CDD whose socket_id matches and whose
> + * socket-local ordinal is @local.
> + *
> + * Return -ENODEV if the cache is unavailable or no CDD matches.
> + */
> +static int phys_nid_to_df_node(unsigned int phys_nid)
> +{
> +	unsigned int socket, local, ordinal = 0;
> +	u16 i;
> +
> +	socket = FIELD_GET(NODE_ID_SOCKET, phys_nid);
> +	local = FIELD_GET(NODE_ID_LOCAL, phys_nid);

Minor nit: align on the '='.

> +
> +	if (!df_cache.nodes)
> +		return -ENODEV;
> +
> +	for (i = 0; i < df_cache.num_cdd; i++) {
> +		if (df_cache.nodes[i].socket_id != socket)
> +			continue;
> +
> +		if (ordinal++ == local)
> +			return i;
> +	}
> +
> +	return -ENODEV;
> +}
> +
>  static int __init build_cache(void)
>  {
>  	struct df_node_cache cache = { };
> @@ -536,6 +576,21 @@ int hygon_node_get_info(u16 node, struct hygon_node_info *info)
>  }
>  EXPORT_SYMBOL_GPL(hygon_node_get_info);
>  
> +static int __maybe_unused cpu_to_df_node(unsigned int cpu)
> +{
> +	if (cpu >= nr_cpu_ids)
> +		return -EINVAL;
> +
> +	/*
> +	 * The NodeId reported by CPUID in a guest may not describe the
> +	 * physical DF topology.
> +	 */
> +	if (cpu_feature_enabled(X86_FEATURE_HYPERVISOR))
> +		return -ENODEV;
> +
> +	return phys_nid_to_df_node(topology_amd_node_id(cpu));
> +}
> +
>  struct pci_dev *hygon_node_get_func(u16 node, u8 func)
>  {
>  	if (!df_cache.nodes)
> -- 

Reviewed-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>

Thanks,
Yazen