linux-kernel - Re: [PATCH v3 4/4] cacheinfo: Add use_arch[|_cache]

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Date:   Thu, 13 Apr 2023 10:49:52 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     linux-kernel@...r.kernel.org, Radu Rendec <rrendec@...hat.com>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Will Deacon <will@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 4/4] cacheinfo: Add use_arch[|_cache]_info
 field/function

On Thu, Apr 13, 2023 at 11:14:34AM +0200, Pierre Gondois wrote:
> The cache information can be extracted from either a Device
> Tree (DT), the PPTT ACPI table, or arch registers (clidr_el1
> for arm64).
> 
> The clidr_el1 register is used only if DT/ACPI information is not
> available. It does not states how caches are shared among CPUs.
> 
> Add a use_arch_cache_info field/function to identify when the
> DT/ACPI doesn't provide cache information. Use this information
> to assume L1 caches are privates and L2 and higher are shared among
> all CPUs.
>

I have tentatively merged first 3 patches along with Radu's series(waiting
for build tests still before confirming). I am not yet sure on this.

> Signed-off-by: Pierre Gondois <pierre.gondois@....com>
> ---
>  drivers/base/cacheinfo.c  | 13 ++++++++++++-
>  include/linux/cacheinfo.h | 10 ++++++++++
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index 06de9a468958..49dbb4357911 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -40,7 +40,8 @@ static inline bool cache_leaves_are_shared(struct cacheinfo *this_leaf,
>  	 * For non DT/ACPI systems, assume unique level 1 caches,
>  	 * system-wide shared caches for all other levels.
>  	 */
> -	if (!(IS_ENABLED(CONFIG_OF) || IS_ENABLED(CONFIG_ACPI)))
> +	if (!(IS_ENABLED(CONFIG_OF) || IS_ENABLED(CONFIG_ACPI)) ||
> +	    this_leaf->use_arch_info)

Can't we just use use_arch_cache_info() here ?

>  		return (this_leaf->level != 1) && (sib_leaf->level != 1);
>  
>  	if ((sib_leaf->attributes & CACHE_ID) &&
> @@ -349,6 +350,7 @@ static int cache_shared_cpu_map_setup(unsigned int cpu)
>  	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
>  	struct cacheinfo *this_leaf, *sib_leaf;
>  	unsigned int index, sib_index;
> +	bool use_arch_info = false;
>  	int ret = 0;
>  
>  	if (this_cpu_ci->cpu_map_populated)
> @@ -361,6 +363,12 @@ static int cache_shared_cpu_map_setup(unsigned int cpu)
>  	 */
>  	if (!last_level_cache_is_valid(cpu)) {
>  		ret = cache_setup_properties(cpu);
> +		if (ret && use_arch_cache_info()) {
> +			// Possibility to rely on arch specific information.
> +			use_arch_info = true;
> +			ret = 0;
> +		}
> +
>  		if (ret)
>  			return ret;
>  	}
> @@ -370,6 +378,9 @@ static int cache_shared_cpu_map_setup(unsigned int cpu)
>  
>  		this_leaf = per_cpu_cacheinfo_idx(cpu, index);
>  
> +		if (use_arch_info)
> +			this_leaf->use_arch_info = true;
> +
>  		cpumask_set_cpu(cpu, &this_leaf->shared_cpu_map);
>  		for_each_online_cpu(i) {
>  			struct cpu_cacheinfo *sib_cpu_ci = get_cpu_cacheinfo(i);
> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> index 908e19d17f49..fed675b251a2 100644
> --- a/include/linux/cacheinfo.h
> +++ b/include/linux/cacheinfo.h
> @@ -66,6 +66,7 @@ struct cacheinfo {
>  #define CACHE_ALLOCATE_POLICY_MASK	\
>  	(CACHE_READ_ALLOCATE | CACHE_WRITE_ALLOCATE)
>  #define CACHE_ID		BIT(4)
> +	bool use_arch_info;

Do you see the need to stash this value as it is either globally true or
false based on the arch ?

>  	void *fw_token;
>  	bool disable_sysfs;
>  	void *priv;
> @@ -129,4 +130,13 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
>  	return -1;
>  }
>  
> +static inline bool use_arch_cache_info(void)
> +{
> +#if defined(CONFIG_ARM64)
> +	return true;
> +#else
> +	return false;
> +#endif
> +}
> +

Can we just have it as:
#ifdef CONFIG_ARM64
#define use_arch_cache_info()	(true)
#else
#define use_arch_cache_info()	(false)
#endif

>  #endif /* _LINUX_CACHEINFO_H */
> -- 
> 2.25.1
> 

-- 
Regards,
Sudeep