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 09:50:49 -0500
From:	Rob Herring <robherring2@...il.com>
To:	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-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 <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 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.

> ---
>  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.

Rob

> +		return NULL;
> +
> +	if (WARN_ON(of_property_read_u32(cpus, "#address-cells", &ac)))
> +		ac = of_n_addr_cells(cpus);
> +
> +	for_each_child_of_node(cpus, cpun) {
> +		if (of_node_cmp(cpun->type, "cpu"))
> +			continue;
> +		cell = of_get_property(cpun, "reg", &prop_len);
> +		if (WARN(!cell, "%s: missing reg property\n", cpun->full_name))
> +			continue;
> +
> +		while (prop_len) {
> +			hwid = of_read_number(cell, ac);
> +			prop_len -= ac;
> +			if (arch_match_cpu_phys_id(cpu, hwid))
> +				return cpun;
> +		}
> +	}
> +
> +	return NULL;
> +}

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