linux-kernel - Re: [PATCH] x86/topology: Add missing declarations and attribute dependencies

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Message-ID: <20260115234346.GA11754@ranerica-svr.sc.intel.com>
Date: Thu, 15 Jan 2026 15:43:46 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/topology: Add missing declarations and attribute
 dependencies

On Mon, Nov 17, 2025 at 08:50:50PM -0800, Ricardo Neri wrote:
> The prototypes for get_topology_cpu_type_name() and
> get_topology_cpu_type() take a pointer to struct cpuinfo_x86, but
> asm/topology.h does not include nor forward-declares the structure. A
> translation unit that includes asm/topology.h, directly or indirectly,
> without including asm/processor.h triggers a warning:
> 
>      ./arch/x86/include/asm/topology.h:159:47: error: ‘struct cpuinfo_x86’
>      declared inside parameter list will not be visible outside of this
>      definition or declaration [-Werror]
>      159 | const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
>          |                                               ^~~~~~~~~~~
> 
> Since only a pointer is needed and no structure members are accessed,
> add a forward declaration of struct cpuinfo_x86.
> 
> Similarly, sysctl_sched_itmt_enabled is declared in asm/topology.h with
> the __read_mostly attribute, but the header does not include linux/cache.h.
> This causes a build failure when a file includes asm/topology.h without
> including linux/cache.h:
> 
>      ./arch/x86/include/asm/topology.h:264:27: error: expected ‘=’, ‘,’,
>       ‘;’, ‘asm’ or ‘__attribute__’ before ‘sysctl_sched_itmt_enabled’
>      264 | extern bool __read_mostly sysctl_sched_itmt_enabled;
>          |                           ^~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Include the needed header.
> 
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
> I found this issue while working on a patchset for Hyper-V support [1]. In
> that case, the file arch/x86/hyperv/hv_vtl.c would now include asm/acpi.h,
> which implicitly includes asm/topology.h but not asm/processor.h nor linux/
> cache.h.
> 
> [1]. https://lore.kernel.org/r/20251117-rneri-wakeup-mailbox-v7-0-4a8b82ab7c2c@linux.intel.com

Hi,

I incorporated this patch in a new version of my patchset to use the ACPI
mailbox with Device-Tree based firmware. It can be found here:

https://lore.kernel.org/r/20260107-rneri-wakeup-mailbox-v8-0-2f5b6785f2f5@linux.intel.com

Thanks and BR,
Ricardo