linux-kernel - Re: [PATCH v8 04/13] arm64/acpi: Create arch specific cpu to acpi id helper

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Date:   Thu, 26 Apr 2018 13:33:14 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Sudeep Holla <sudeep.holla@....com>, linux-acpi@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org, Lorenzo.Pieralisi@....com,
        hanjun.guo@...aro.org, rjw@...ysocki.net, Will.Deacon@....com,
        Catalin.Marinas@....com, gregkh@...uxfoundation.org,
        Mark.Rutland@....com, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, wangxiongfeng2@...wei.com,
        vkilari@...eaurora.org, ahs3@...hat.com, Dietmar.Eggemann@....com,
        Morten.Rasmussen@....com, palmer@...ive.com, lenb@...nel.org,
        john.garry@...wei.com, austinwc@...eaurora.org,
        tnowicki@...iumnetworks.com, jhugo@....qualcomm.com,
        timur@....qualcomm.com, ard.biesheuvel@...aro.org
Subject: Re: [PATCH v8 04/13] arm64/acpi: Create arch specific cpu to acpi id
 helper

Hi,

On 04/26/2018 05:27 AM, Sudeep Holla wrote:
> 
> 
> On 26/04/18 00:31, Jeremy Linton wrote:
>> Its helpful to be able to lookup the acpi_processor_id associated
>> with a logical cpu. Provide an arm64 helper to do this.
>>
> 
> As I pointed out in the earlier version, this patch is not required.
> The acpi_id stored in the acpi_processor can be used for this.
> Won't the below change make it work ? I can't think of any reason why it
> shouldn't.

So, I only noticed your previous email last night on the mail archive, 
as I was applying your review/ack tags and couldn't find a response for 
this patch, seem the spam/etc filters need some further tweaking!

At that point, I was pretty sure the suggestion wasn't going to work out 
of the box as a lot of this code is running fairly early in the boot 
process. I spent a bit of time and plugged the change in to verify that 
assertion, and yes the per_cpu processor/acpi bits aren't setup early 
enough to be used by much of this code. It is being called from 
init_cpu_topology()/smp_prepare_cpus() which precedes 
do_basic_setup/do_initcalls() which is what runs the acpi_init() 
sequence which ends up eventually allocating the required data 
structures. So without restructuring the core boot sequence, this seems 
like a reasonable solution.


Thanks,


> 
> Regards,
> Sudeep
> 
> -->8
> 
> diff --git i/drivers/acpi/pptt.c w/drivers/acpi/pptt.c
> index 0fc4b2654665..f421f58b4ae6 100644
> --- i/drivers/acpi/pptt.c
> +++ w/drivers/acpi/pptt.c
> @@ -432,7 +432,7 @@ static void cache_setup_acpi_cpu(struct
> acpi_table_header *table,
>   {
>          struct acpi_pptt_cache *found_cache;
>          struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> -       u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> +       u32 acpi_cpu_id = per_cpu(processors, cpu)->acpi_id;
>          struct cacheinfo *this_leaf;
>          unsigned int index = 0;
>          struct acpi_pptt_processor *cpu_node = NULL;
>