linux-kernel - Re: [PATCH v2 2/2] ACPI/PPTT: Handle architecturally unknown cache types

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Message-ID: <71208e0e-fba9-ad6c-7578-a53fd1aa3f40@arm.com>
Date:   Mon, 17 Sep 2018 17:17:07 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jeffrey Hugo <jhugo@...eaurora.org>, gregkh@...uxfoundation.org,
        rjw@...ysocki.net, linux-acpi@...r.kernel.org,
        jeremy.linton@....com
Cc:     Sudeep Holla <sudeep.holla@....com>, linux-kernel@...r.kernel.org,
        vkilari@...eaurora.org
Subject: Re: [PATCH v2 2/2] ACPI/PPTT: Handle architecturally unknown cache
 types



On 14/09/18 17:28, Jeffrey Hugo wrote:
> The type of a cache might not be specified by architectural mechanisms (ie
> system registers), but its type might be specified in the PPTT.  In this
> case, we should populate the type of the cache, rather than leave it
> undefined.
> 
> This fixes the issue where the cacheinfo driver will not populate sysfs
> for such caches, resulting in the information missing from utilities like
> lstopo and lscpu, thus degrading the user experience.
> 
> Fixes: 2bd00bcd73e5 (ACPI/PPTT: Add Processor Properties Topology Table parsing)
> Reported-by: Vijaya Kumar K <vkilari@...eaurora.org>
> Signed-off-by: Jeffrey Hugo <jhugo@...eaurora.org>
> ---
>  drivers/acpi/pptt.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index d1e26cb..bb00ed9 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -402,11 +402,18 @@ static void update_cache_properties(struct cacheinfo *this_leaf,
>  		}
>  	}
>  	/*
> -	 * If the above flags are valid, and the cache type is NOCACHE
> -	 * update the cache type as well.
> +	 * If cache type is NOCACHE, then the cache hasn't been specified
> +	 * via other mechanisms.  Update the type if either the cache has
> +	 * been fully specified in PPTT, or a cache type has been provided.
> +	 *
> +	 * Note, we assume such caches are unified based on conventional system
> +	 * design and known examples.  Significant work is required elsewhere to
> +	 * fully support data/instruction only type caches which are only
> +	 * specified in PPTT.
>  	 */
> -	if (this_leaf->type == CACHE_TYPE_NOCACHE &&
> -	    valid_flags == PPTT_CHECKED_ATTRIBUTES)
> +	if ((this_leaf->type == CACHE_TYPE_NOCACHE) &&
> +	    (valid_flags == PPTT_CHECKED_ATTRIBUTES ||
> +	     found_cache->flags & ACPI_PPTT_CACHE_TYPE_VALID))
>  		this_leaf->type = CACHE_TYPE_UNIFIED;

I thought I did mention that we can drop the valid_flags altogether
unless Jeremy has reasons not to.

-- 
Regards,
Sudeep