linux-kernel - Re: [PATCH v3 01/16] of: add support for retrieving cpu node for a given logical cpu index

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Date:	Mon, 22 Jul 2013 10:14:02 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	devicetree@...r.kernel.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 <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 01/16] of: add support for retrieving cpu node for a
 given logical cpu index

On Mon, 22 Jul 2013, Sudeep KarkadaNagesha 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.
> 
> Acked-by: Rob Herring <rob.herring@...xeda.com>
> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>

Minor nits below.  Otherwise...

Acked-by: Nicolas Pitre <nico@...aro.org>

> ---
>  drivers/of/base.c  | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/of.h |  6 +++++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 5c54279..1e690bf 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -230,6 +230,78 @@ 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 architecture specific.
> + * However this __weak function provides a default match of physical
> + * id to logical cpu index.
> + *
> + * Returns true if the physical identifier and the logical index correspond
> + * to the same cpu, false otherwise.
> + */
> +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id)

Maybe a prototype declaration for this function should be added to 
include/linux/of.h to avoid mismatch with architecture provided 
versions.

> +{
> +	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 intialize the of_node in

s/intialize/initialize/


Nicolas
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