linux-kernel - Re: [PATCH v8 07/13] drivers: base cacheinfo: Add support for ACPI based firmware tables

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Date:   Thu, 26 Apr 2018 13:57:00 -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 07/13] drivers: base cacheinfo: Add support for ACPI
 based firmware tables

Hi,

On 04/26/2018 06:05 AM, Sudeep Holla wrote:
> 
> 
> On 26/04/18 00:31, Jeremy Linton wrote:
>> Call ACPI cache parsing routines from base cacheinfo code if ACPI
>> is enable. Also stub out cache_setup_acpi() so that individual
>> architectures can enable ACPI topology parsing.
>>
> 
> [...]
> 
>> +#ifndef CONFIG_ACPI
>> +static inline int acpi_find_last_cache_level(unsigned int cpu)
>> +{
>> +	/* ACPI kernels should be built with PPTT support */
> 
> This sounds incorrect for x86. But I understand why you have it there.
> Does it makes sense to change above to .. ?
> 
> #if !defined(CONFIG_ACPI) || (defined(CONFIG_ACPI) && !(CONFIG_ACPI_PPTT))
> 
I'm not sure what that buys us, if anything you want more non-users of 
the function to be falling through to the function prototype rather than 
the static inline. The only place any of this matters (as long as the 
compiler/linker is tossing the static inline) is arm64 because its the 
only arch making a call to acpi_find_last_cache_level(). ACPI_PPTT is 
also only visible on arm64 at the moment due to being wrapped in a if 
ARM64 in the Kconfig

Put another way, I wouldn't expect an arch to have a 'user' visible 
option to enable/disable parsing the PPTT. If an arch can handle 
ACPI/PPTT topology then I would expect it to be fixed to the CONFIG_ACPI 
state. What happens when acpi_find_last_cache_level() is called should 
only be dependent on whether ACPI is enabled, the PPTT parser itself 
will handle the cases of a missing table.