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

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Message-ID: <4b50b3e9-55d7-67c7-dbaf-8bd7d7fb23a5@arm.com>
Date:   Mon, 17 Sep 2018 17:59:19 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Sudeep Holla <sudeep.holla@....com>,
        gregkh@...uxfoundation.org, rjw@...ysocki.net,
        linux-acpi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, vkilari@...eaurora.org
Subject: Re: [PATCH v2 2/2] ACPI/PPTT: Handle architecturally unknown cache
 types

Hi,

On 09/17/2018 05:46 PM, Jeffrey Hugo wrote:
> On 9/17/2018 10:17 AM, Sudeep Holla wrote:
>>
>>
>> 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.
>>
> 
> You suggested that perhaps that could be the case.  It seemed like an 
> open question to me.  I'm at Linaro Connect without access to the device 
> this week, so I guess someone has roughly a week to chime in that the 
> valid flags should be kept, otherwise I'll try a v3 with them removed.
> 

The point of the valid_flags/CHECKED_ATTRIBUTE was to help assure that a 
minimum set of attributes were being provided by the firmware. If we are 
going to reset the CACHE_TYPE, then we might as well remove the 
valid_flag/CHECKED_ATTRIBUTE counts as it can be easily bypassed.

So, yes please, remove the valid_flags with this change.

Thanks,