linux-kernel - Re: [PATCH v2 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

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Message-ID: <2d1b547f-f9ee-391c-c4f3-0232a08a86bc@arm.com>
Date:   Tue, 18 Jun 2019 09:21:21 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Valentin Schneider <valentin.schneider@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, will.deacon@....com, rjw@...ysocki.net,
        sudeep.holla@....com, lenb@...nel.org
Subject: Re: [PATCH v2 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

On 6/17/19 7:34 AM, Valentin Schneider wrote:
> Hi Jeremy,
> 
> Few nits below.
> 
> Also, I had a look at the other PPTT processor flags that were introduced
> in 6.3, and the only other one being used is ACPI_LEAF_NODE in
> acpi_pptt_leaf_node(). However that one already has a handle on the table
> header, so the check_acpi_cpu_flag() isn't of much help there.
> 
> I don't believe the other existing flags will benefit from the helper since
> they are more about describing the PPTT tree, but I think it doesn't hurt
> to keep it around for potential future flags.

That was the thought process.

> 
> On 14/06/2019 23:31, Jeremy Linton wrote:
> [...]
>> @@ -517,6 +517,43 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
>>   	return retval;
>>   }
>>   
>> +/**
>> + * check_acpi_cpu_flag() - Determine if CPU node has a flag set
>> + * @cpu: Kernel logical CPU number
>> + * @rev: The PPTT revision defining the flag
>> + * @flag: The flag itself
>> + *
>> + * Check the node representing a CPU for a given flag.
>> + *
>> + * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
>> + *	   the table revision isn't new enough.
>> + * Otherwise returns flag value
>> + */
> 
> Nit: strictly speaking we're not returning the flag value but its mask
> applied to the flags field. I don't think anyone will care about getting
> the actual flag value, but it should be made obvious in the doc:

Or I clarify the code to actually do what the comments says. Maybe that 
is what John G was also pointing out too?


> 
> -ENOENT if ...
> 0 if the flag isn't set
>> 0 if it is set.
> 
> [...]
>> @@ -581,6 +618,21 @@ int cache_setup_acpi(unsigned int cpu)
>>   	return status;
>>   }
>>   
>> +/**
>> + * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
>> + * @cpu: Kernel logical CPU number
>> + *
>> + *
> 
> Nit: extra newline
> 
>> + * Return: 1, a thread
>> + *         0, not a thread
>> + *         -ENOENT ,if the PPTT doesn't exist, the CPU cannot be found or
>> + *         the table revision isn't new enough.
>> + */
>> +int acpi_pptt_cpu_is_thread(unsigned int cpu)
>> +{
>> +	return check_acpi_cpu_flag(cpu, 2, ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD);
>> +}
>> +
>>   /**
>>    * find_acpi_cpu_topology() - Determine a unique topology value for a given CPU
>>    * @cpu: Kernel logical CPU number
>> @@ -641,7 +693,6 @@ int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
> [...]
>