linux-kernel - Re: [PATCH 1/3] topology/sysfs: export die attributes only if an architectures has support

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Message-ID: <YaR5AuPPq2kODFfI@kroah.com>
Date:   Mon, 29 Nov 2021 07:53:54 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Len Brown <len.brown@...el.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH 1/3] topology/sysfs: export die attributes only if an
 architectures has support

On Sun, Nov 28, 2021 at 10:22:19PM +0100, Heiko Carstens wrote:
> The die_id and die_cpus topology sysfs attributes have been added with
> commit 0e344d8c709f ("cpu/topology: Export die_id") and commit
> 2e4c54dac7b3 ("topology: Create core_cpus and die_cpus sysfs attributes").
> 
> While they are currently only used and useful for x86 they are still
> present with bogus default values for all architectures. Instead of
> enforcing such new sysfs attributes to all architectures, make them
> only optional visible if an architecture opts in by defining both the
> topology_die_id and topology_die_cpumask attributes.
> 
> This is similar to what was done when the book and drawer topology
> levels were introduced: avoid useless and therefore confusing sysfs
> attributes for architectures which cannot make use of them.
> 
> This should not break any existing applications, since this is a
> rather new interface and applications should be able to handle also
> older kernel versions without such attributes - besides that they
> contain only useful information for x86.
> 
> Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
> ---
>  Documentation/admin-guide/cputopology.rst | 3 +++
>  drivers/base/topology.c                   | 8 ++++++++
>  include/linux/topology.h                  | 2 ++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst
> index 6b62e182baf4..c68d07533c45 100644
> --- a/Documentation/admin-guide/cputopology.rst
> +++ b/Documentation/admin-guide/cputopology.rst
> @@ -11,6 +11,9 @@ Architecture-neutral, drivers/base/topology.c, exports these attributes.
>  However, the book and drawer related sysfs files will only be created if
>  CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are selected, respectively.
>  
> +The die hierarchy related sysfs files will only be created if an architecture
> +provides the related macros as described below.
> +
>  CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are currently only used on s390,
>  where they reflect the cpu and cache hierarchy.
>  
> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
> index 8f2b641d0b8c..7fa5a7fbef25 100644
> --- a/drivers/base/topology.c
> +++ b/drivers/base/topology.c
> @@ -45,8 +45,10 @@ static ssize_t name##_list_read(struct file *file, struct kobject *kobj,	\
>  define_id_show_func(physical_package_id);
>  static DEVICE_ATTR_RO(physical_package_id);
>  
> +#ifndef topology_die_no_sysfs

Please flip this #define around to be the other way:
	TOPOLOGY_DIE_SYSFS
and enable/disable it.

Makes it much easier to understand than "negative logic"

Also, defines need to be all uppercase.

thanks,

greg k-h