linux-kernel - Re: [PATCH v2 2/6] of: Add helper for mapping device node to logical CPU number

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Date:   Tue, 25 Jul 2017 10:27:31 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     mark.rutland@....com, peterz@...radead.org, will.deacon@....com,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v2 2/6] of: Add helper for mapping device node to logical
 CPU number

On 24/07/17 17:42, Sudeep Holla wrote:
>
>
> On 24/07/17 11:29, Suzuki K Poulose wrote:
>> Add a helper to map a device node to a logical CPU number to avoid
>> duplication. Currently this is open coded in different places (e.g
>> gic-v3, coresight). The helper tries to map device node to a "possible"
>> logical CPU id, which may not be online yet. It is the responsibility
>> of the user to make sure that the CPU is online. The helper uses
>> of_get_cpu_node() which uses arch specific backends to match the phyiscal
>> ids.
>>
>> Cc: Rob Herring <robh+dt@...nel.org>
>> Cc: Mark Rutland <mark.rutland@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>  drivers/of/base.c         | 26 ++++++++++++++++++++++++++
>>  include/linux/of_device.h |  7 +++++++
>>  2 files changed, 33 insertions(+)
>>
>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>> index 686628d..639af23 100644
>> --- a/drivers/of/base.c
>> +++ b/drivers/of/base.c
>> @@ -420,6 +420,32 @@ struct device_node *of_get_cpu_node(int cpu, unsigned int *thread)
>>  EXPORT_SYMBOL(of_get_cpu_node);
>>
>>  /**
>> + * of_device_node_get_cpu: Get the logical CPU number for a given device_node
>> + *
>> + * @cpu_node: Pointer to the device_node for CPU.
>> + *
>> + * Returns the logical CPU number of the given CPU device_node.
>> + * Returns >= nr_cpu_ids if CPU is not found.
>> + */
>> +int of_device_node_get_cpu(struct device_node *cpu_node)
>> +{
>> +	int cpu, thread;
>> +	bool found = false;
>> +	struct device_node *np;
>> +
>> +	for_each_possible_cpu(cpu) {
>> +		np = of_get_cpu_node(cpu, &thread);
>
> Ideally, we should be able to use of_cpu_device_node_get instead of
> of_get_cpu_node which parses the device tree. Not sure if that's the
> case here too.
>
> Sorry for following up on this so late. I had a patch in my tree
> for-a-while to address that. Just posted it[1] now seeing this patch now.
>
> You can move to of_cpu_device_node_get if all users of this function are
> called after CPU's are registered. Otherwise, you can keep it as is for
> now and it can be changed once [1] lands.

As you mentioned offline, since GIC uses this, we need to stick to of_get_cpu_node.
In fact, I started off with the of_cpu_device_node_get() and switched to the former.

It would be really nice to have your patch, which streamlines the interface and we
could switch to that.

Cheers
Suzuki

>