linux-kernel - Re: [RFC PATCH v2 01/15] of: add support for retrieving cpu node for a given logical cpu index

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Date:	Wed, 17 Jul 2013 16:18:17 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Rob Herring <robherring2@...il.com>
CC:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Russell King <linux@....linux.org.uk>,
	Shawn Guo <shawn.guo@...aro.org>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH v2 01/15] of: add support for retrieving cpu node
 for a given logical cpu index

On 17/07/13 15:50, Rob Herring wrote:
> On 07/17/2013 09:06 AM, Sudeep.KarkadaNagesha@....com wrote:
>> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
>>
>> Currently different drivers requiring to access cpu device node are
>> parsing the device tree themselves. Since the ordering in the DT need
>> not match the logical cpu ordering, the parsing logic needs to consider
>> that. However, this has resulted in lots of code duplication and in some
>> cases even incorrect logic.
>>
>> It's better to consolidate them by adding support for getting cpu
>> device node for a given logical cpu index in DT core library. However
>> logical to physical index mapping can be architecture specific.
>>
>> This patch adds of_get_cpu_node to retrieve a cpu device node for a
>> given logical cpu index. The default matching of the physical id to the
>> logical cpu index can be overridden by architecture specific code.
>>
>> It is recommended to use these helper function only in pre-SMP/early
>> initialisation stages to retrieve CPU device node pointers in logical
>> ordering. Once the cpu devices are registered, it can be retrieved easily
>> from cpu device of_node which avoids unnecessary parsing and matching.
>>
>> Cc: Rob Herring <rob.herring@...xeda.com>
>> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>
> 
> One comment below, but otherwise for patches 1-4, 8 and 9:
> 
> Acked-by: Rob Herring <rob.herring@...xeda.com>
> 
> Also, patch 3 needs to come before patch 2 or the matching will be wrong
> if patch 3 is not applied.
Ah, correct will fix it in next version.

> 
>> ---
>>  drivers/of/base.c  | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/of.h |  5 +++++
>>  2 files changed, 71 insertions(+)
>>
>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>> index 5c54279..363b8f9 100644
>> --- a/drivers/of/base.c
>> +++ b/drivers/of/base.c
>> @@ -230,6 +230,72 @@ const void *of_get_property(const struct device_node *np, const char *name,
>>  }
>>  EXPORT_SYMBOL(of_get_property);
>>  
>> +/*
>> + * arch_match_cpu_phys_id - Match the given logical CPU and physical id
>> + *
>> + * @cpu: logical index of a cpu
>> + * @phys_id: physical identifier of a cpu
>> + *
>> + * CPU logical to physical index mapping is architecure specific.
>> + * However this __weak function provides a default match of physical
>> + * id to logical cpu index.
>> + *
>> + * Returns 1 if the physical identifier and the logical index correspond
>> + * to the same cpu, 0 otherwise.
>> + */
>> +int __weak arch_match_cpu_phys_id(int cpu, u64 phys_id)
>> +{
>> +	return (u32)phys_id == cpu;
>> +}
>> +
>> +/**
>> + * of_get_cpu_node - Get device node associated with the given logical CPU
>> + *
>> + * @cpu: CPU number(logical index) for which device node is required
>> + *
>> + * The main purpose of this function is to retrieve the device node for the
>> + * given logical CPU index. It should be used to intialise the of_node in
>> + * cpu device. Once of_node in cpu device is populated, all the further
>> + * references can use that instead.
>> + *
>> + * CPU logical to physical index mapping is architecure specific and is built
>> + * before booting secondary cores. This function uses arch_match_cpu_phys_id
>> + * which can be overridden by architecture specific implementation.
>> + *
>> + * Returns a node pointer for the logical cpu if found, else NULL.
>> + */
>> +struct device_node *of_get_cpu_node(int cpu)
>> +{
>> +	struct device_node *cpun, *cpus;
>> +	const u32 *cell;
>> +	u64 hwid;
>> +	int ac, prop_len;
>> +
>> +	cpus = of_find_node_by_path("/cpus");
>> +	if (WARN(!cpus, "Missing cpus node, bailing out\n"))
> 
> What happens on a system with no /cpus nodes? Seems like this is another
> case of adding new warnings to existing working systems.
> 
> I'd replace all the WARN's with a single pr_warn on any errors below.
> For missing /cpus, I would just silently return.

Ah, forgot recent discussions on this, will fix it.

Regards,
Sudeep

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