RE: [PATCH v3 1/3] xen/device-tree: Parse 'cpu-map' node for CPU topology exploration

[Hirokazu Takahashi <taka@xxxxxxxxxxxxx>]

Hello,

> Subject: Re: [PATCH v3 1/3] xen/device-tree: Parse 'cpu-map' node for CPU
> topology exploration
> 
> On 01.07.2026 13:11, Hirokazu Takahashi wrote:
> >>> +static unsigned int __init get_cpu_for_node(struct dt_device_node
> *node)
> >>
> >> Pointer-to-const?
> >
> > Do you mean this should be replaced with the following line?
> > static unsigned int __init get_cpu_for_node(struct dt_device_node *const
> node)
> 
> No, that's a const pointer-to-something.
> 
> static unsigned int __init get_cpu_for_node(const struct dt_device_node *node)

Understood.
 
> >>> +#else /* CONFIG_CPU_TOPOLOGY */
> >>> +
> >>> +#define cpu_topology ((struct cpu_topology *)NULL)
> >>
> >> Why exactly is this needed? It very much looks as if its presence may hide
> bugs.
> >
> > In the current code, the condition if ( cpu_topology ) is used to cover both
> cases:
> > when CONFIG_CPU_TOPOLOGY is disabled, and when memory allocation for
> > topology table fails.
> >
> > The next patch uses if ( cpu_topology ).
> >
> > static int setup_cpu_sibling_map(int cpu)
> > {
> >     if ( !zalloc_cpumask_var(&per_cpu(cpu_sibling_mask, cpu)) ||
> >          !zalloc_cpumask_var(&per_cpu(cpu_core_mask, cpu)) )
> >         return -ENOMEM;
> >
> >     if ( cpu_topology )
> 
>     if ( IS_ENABLED(CONFIG_GENERIC_CPU_TOPOLOGY) )

This line should be if ( IS_ENABLED(CONFIG_GENERIC_CPU_TOPOLOGY) && 
cpu_topology )
because 'cpu_topology' can be NULL even if CONFIG_GENERIC_CPU_TOPOLOGY is on.

void __init init_cpu_topology(void)
{
    unsigned int cpu;

    cpu_topology = xzalloc_array(struct cpu_topology, nr_cpu_ids);
    if ( !cpu_topology )
    {
        printk(XENLOG_ERR "Failed to allocate memory for cpu_topology table\n");
        return;
    }
        :
        :

Thank you,
Hirokazu Takahashi.