linux-kernel - Re: [PATCH v5 03/34] ACPI / PPTT: Add acpi_pptt_cache_v1

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Message-ID: <bef76508-830c-497d-a539-6110686b412f@nvidia.com>
Date: Tue, 18 Nov 2025 08:30:08 -0800
From: Fenghua Yu <fenghuay@...dia.com>
To: Ben Horgan <ben.horgan@....com>, james.morse@....com
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, bobo.shaobowang@...wei.com,
 carl@...amperecomputing.com, catalin.marinas@....com, dakr@...nel.org,
 dave.martin@....com, david@...hat.com, dfustini@...libre.com,
 gregkh@...uxfoundation.org, gshan@...hat.com, guohanjun@...wei.com,
 jeremy.linton@....com, jonathan.cameron@...wei.com, kobak@...dia.com,
 lcherian@...vell.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 lpieralisi@...nel.org, peternewman@...gle.com, quic_jiles@...cinc.com,
 rafael@...nel.org, robh@...nel.org, rohit.mathew@....com,
 scott@...amperecomputing.com, sdonthineni@...dia.com, sudeep.holla@....com,
 tan.shaopeng@...itsu.com, will@...nel.org, xhao@...ux.alibaba.com
Subject: Re: [PATCH v5 03/34] ACPI / PPTT: Add acpi_pptt_cache_v1_full to use
 pptt cache as one structure



On 11/18/25 02:57, Ben Horgan wrote:
> Hi Fenghua,
> 
> On 11/18/25 04:03, Fenghua Yu wrote:
>> Hi, Ben,
>>
>> On 11/17/25 08:59, Ben Horgan wrote:
>>> In actbl2.h, acpi_pptt_cache describes the fields in the original
>>> Cache Type Structure. In PPTT table version 3 a new field was added at
>>> the
>>> end, cache_id. This is described in acpi_pptt_cache_v1 but rather than
>>> including all v1 fields it just includes this one.
>>>
>>> In lieu of this being fixed in acpica, introduce
>>> acpi_pptt_cache_v1_full to
>>> contain all the fields of the Cache Type Structure . Update the existing
>>> code to use this new struct. This simplifies the code and removes a
>>> non-standard use of ACPI_ADD_PTR.
>>>
>>> Signed-off-by: Ben Horgan <ben.horgan@....com>
>>> ---
>>> I have opened a pull request to acpica to update acpi_pptt_cache_v1 to
>>> include all fields. https://github.com/acpica/acpica/pull/1059
>>>
>>> Change since v4:
>>> Use fields directly in acpi_pptt_cache_v1_full
>>> Delay the casting
>>>
>>> Changes since v3:
>>> New patch
>>> ---
>>>    drivers/acpi/pptt.c | 47 +++++++++++++++++++++++++++++++++++----------
>>>    1 file changed, 37 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>>> index 2856254e29d7..53fde9bd8140 100644
>>> --- a/drivers/acpi/pptt.c
>>> +++ b/drivers/acpi/pptt.c
>>> @@ -21,6 +21,25 @@
>>>    #include <linux/cacheinfo.h>
>>>    #include <acpi/processor.h>
>>>    +/*
>>> + * The acpi_pptt_cache_v1 in actbl2.h, which is imported from acpica,
>>> + * only contains the cache_id field rather than all the fields of the
>>> + * Cache Type Structure. Use this alternative structure until it is
>>> + * resolved in acpica.
>>> + */
>>> +struct acpi_pptt_cache_v1_full {
>>> +    struct acpi_subtable_header header;
>>> +    u16 reserved;
>>> +    u32 flags;
>>> +    u32 next_level_of_cache;
>>> +    u32 size;
>>> +    u32 number_of_sets;
>>> +    u8 associativity;
>>> +    u8 attributes;
>>> +    u16 line_size;
>>> +    u32 cache_id;
>>> +};
>>
>> Should "__packed" be added to this table?
> 
> Yes, I missed that.
> 

With this fixed,

Reviewed-by: Fenghua Yu <fenghuay@...dia.com>

>>
>> Should this table be defined in include/acpi/actbl2.h? Seems defining
>> the two cache tables separately in two places are not natural?
> 
> Indeed. The dificulty is that include/acpi/actbl2.h is generated from
> acpica. I propose a fix for this in the  pull request mentioned above:
> https://github.com/acpica/acpica/pull/1059 This extends
> acpi_pptt_cache_v1 to include all the fields in the new version of the
> cache type structure (not just cache_id).
> 
> One thing I could do if it looks like the acpica change will be accepted
> is to temporarily delete acpi_pptt_cache_v1 from include/acpi/actbl2.h
> and rename acpi_pptt_cache_v1_full in drivers/acpi/pptt.c to
> acpi_pptt_cache_v1. When include/acpi/actbl2.h is updated the conflict
> should be evident and the version in drivers/acpi/pptt.c can be dropped.
>   I'll keep it like it is for now though as this would be an api breaking
> change for acpica and the maintainers may prefer to handle this a
> different way.

Right. Thank you for your explanation!

-Fenghua