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 10:49:24 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Sudeep Holla <sudeep.holla@....com>, 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 25/07/17 10:27, Suzuki K Poulose wrote:
> 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.

Agreed.

> In fact, I started off with the of_cpu_device_node_get() and switched
> to the former.
> 

Ah OK.

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

Yes, I will wait for that patch to land in the mainline, I can follow up
and remove the use of of_get_cpu_node wherever required.
-- 
Regards,
Sudeep