linux-kernel - Re: [PATCH 03/33] ACPI / PPTT: Add acpi_pptt_cache_v1

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Message-ID: <374f53a9-6ff5-4c37-bd41-9e746eaec1da@arm.com>
Date: Mon, 10 Nov 2025 15:51:57 +0000
From: Ben Horgan <ben.horgan@....com>
To: Gavin Shan <gshan@...hat.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,
 fenghuay@...dia.com, gregkh@...uxfoundation.org, 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,
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 tan.shaopeng@...itsu.com, will@...nel.org, xhao@...ux.alibaba.com
Subject: Re: [PATCH 03/33] ACPI / PPTT: Add acpi_pptt_cache_v1_full to use
 pptt cache as one structure

Hi Gavin,

On 11/8/25 04:54, Gavin Shan wrote:
> Hi Ben,
> 
> On 11/7/25 10:34 PM, Ben Horgan wrote:
>> In actbl2.h, struct 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 struct acpi_pptt_cache_v1. Introduce
>> the new, acpi_pptt_cache_v1_full to contain both these structures. Update
>> the existing code to use this new struct. This simplifies the code,
>> removes
>> a non-standard use of ACPI_ADD_PTR and allows using the length in the
>> header to check if the cache_id is valid.
>>
>> Signed-off-by: Ben Horgan <ben.horgan@....com>
>> ---
>> Changes since v3:
>> New patch
>> ---
>>   drivers/acpi/pptt.c | 104 ++++++++++++++++++++++++--------------------
>>   1 file changed, 58 insertions(+), 46 deletions(-)
>>
> 
> Two nitpicks below. LGTM in either way.
> 
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> 
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index 1027ca3566b1..1ed2099c0d1a 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -21,6 +21,11 @@
>>   #include <linux/cacheinfo.h>
>>   #include <acpi/processor.h>
>>   +struct acpi_pptt_cache_v1_full {
>> +    struct acpi_pptt_cache        f;
>> +    struct acpi_pptt_cache_v1    extra;
>> +} __packed;
>> +
>>   static struct acpi_subtable_header *fetch_pptt_subtable(struct
>> acpi_table_header *table_hdr,
>>                               u32 pptt_ref)
>>   {
>> @@ -50,10 +55,24 @@ static struct acpi_pptt_processor
>> *fetch_pptt_node(struct acpi_table_header *tab
>>       return (struct acpi_pptt_processor
>> *)fetch_pptt_subtable(table_hdr, pptt_ref);
>>   }
>>   -static struct acpi_pptt_cache *fetch_pptt_cache(struct
>> acpi_table_header *table_hdr,
>> -                        u32 pptt_ref)
>> +static struct acpi_pptt_cache_v1_full *fetch_pptt_cache(struct
>> acpi_table_header *table_hdr,
>> +                            u32 pptt_ref)
>>   {
>> -    return (struct acpi_pptt_cache *)fetch_pptt_subtable(table_hdr,
>> pptt_ref);
>> +    return (struct acpi_pptt_cache_v1_full
>> *)fetch_pptt_subtable(table_hdr, pptt_ref);
>> +}
>> +
>> +#define ACPI_PPTT_CACHE_V1_LEN sizeof(struct acpi_pptt_cache_v1_full)
>> +
>> +/*
>> + * From PPTT table version 3, a new field cache_id was added at the
>> end of
>> + * the cache type structure.  We now use struct acpi_pptt_cache_v1_full,
>> + * containing the cache_id, everywhere but must check validity before
>> accessing
>> + * the cache_id.
>> + */
>> +static bool acpi_pptt_cache_id_is_valid(struct
>> acpi_pptt_cache_v1_full *cache)
>> +{
>> +    return (cache->f.header.length >= ACPI_PPTT_CACHE_V1_LEN &&
>> +        cache->f.flags & ACPI_PPTT_CACHE_ID_VALID);
>>   }
>>   
> 
> This function is nice fit to 'inline'. Besides, I'm not sure if we can just
> use sizeof(*cache) instead of ACPI_PPTT_CACHE_V1_LEN, which is used for
> once
> in pptt.c

Yes, the define is unnecessary and the function can be inlined. Thanks
for pointing it out. I'm likely to rework this patch though.

Thanks,

Ben