[RFC PATCH 1/4] ARM: kernel: add device tree init map function

[robherring2@gmail.com (Rob Herring)]

On 10/16/2012 08:21 AM, Lorenzo Pieralisi wrote:
> When booting through a device tree, the kernel cpu logical id map can be
> initialized using device tree data passed by FW or through an embedded blob.
> 
> This patch adds a function that parses device tree "cpu" nodes and
> retrieves the corresponding CPUs hardware identifiers (MPIDR).
> It sets the possible cpus and the cpu logical map values according to
> the number of CPUs defined in the device tree and respective properties.
> 
> The primary CPU is assigned cpu logical number 0 to keep the current
> convention valid.
> 
> Current bindings documentation is included in the patch:
> 
> Documentation/devicetree/bindings/arm/cpus.txt
> 
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> ---
>  Documentation/devicetree/bindings/arm/cpus.txt | 42 +++++++++++++++++++++++
>  arch/arm/include/asm/prom.h                    |  2 ++
>  arch/arm/kernel/devtree.c                      | 47 ++++++++++++++++++++++++++
>  3 files changed, 91 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/cpus.txt
> 
> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
> new file mode 100644
> index 0000000..897f3b4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> @@ -0,0 +1,42 @@
> +* ARM CPUs binding description
> +
> +The device tree allows to describe the layout of CPUs in a system through
> +the "cpus" node, which in turn contains a number of subnodes (ie "cpu")
> +defining properties for every cpu.
> +
> +Bindings for CPU nodes follow the ePAPR standard, available from:
> +
> +http://devicetree.org
> +
> +For the ARM architecture every CPU node must contain the following property:
> +
> +- reg : property defining the CPU MPIDR[23:0] register bits

defining or matching the MPIDR?

> +
> +Every cpu node is required to set its device_type to "cpu".

This is a bit questionable as device_type is deprecated for FDT.
However, since the ePAPR defines using it

You should add a compatible property for the cpu model.

> +
> +Example:
> +
> +	cpus {
> +		#size-cells = <0>;
> +		#address-cells = <1>;
> +
> +		CPU0: cpu at 0 {
> +			device_type = "cpu";
> +			reg = <0x0>;
> +		};
> +
> +		CPU1: cpu at 1 {
> +			device_type = "cpu";
> +			reg = <0x1>;
> +		};
> +
> +		CPU2: cpu at 100 {
> +			device_type = "cpu";
> +			reg = <0x100>;
> +		};
> +
> +		CPU3: cpu at 101 {
> +			device_type = "cpu";
> +			reg = <0x101>;
> +		};
> +	};
> diff --git a/arch/arm/include/asm/prom.h b/arch/arm/include/asm/prom.h
> index aeae9c6..8dd51dc 100644
> --- a/arch/arm/include/asm/prom.h
> +++ b/arch/arm/include/asm/prom.h
> @@ -15,6 +15,7 @@
>  
>  extern struct machine_desc *setup_machine_fdt(unsigned int dt_phys);
>  extern void arm_dt_memblock_reserve(void);
> +extern void __init arm_dt_init_cpu_maps(void);
>  
>  #else /* CONFIG_OF */
>  
> @@ -24,6 +25,7 @@ static inline struct machine_desc *setup_machine_fdt(unsigned int dt_phys)
>  }
>  
>  static inline void arm_dt_memblock_reserve(void) { }
> +static inline void arm_dt_init_cpu_maps(void) { }
>  
>  #endif /* CONFIG_OF */
>  #endif /* ASMARM_PROM_H */
> diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
> index bee7f9d..c86e414 100644
> --- a/arch/arm/kernel/devtree.c
> +++ b/arch/arm/kernel/devtree.c
> @@ -19,8 +19,10 @@
>  #include <linux/of_irq.h>
>  #include <linux/of_platform.h>
>  
> +#include <asm/cputype.h>
>  #include <asm/setup.h>
>  #include <asm/page.h>
> +#include <asm/smp_plat.h>
>  #include <asm/mach/arch.h>
>  #include <asm/mach-types.h>
>  
> @@ -61,6 +63,51 @@ void __init arm_dt_memblock_reserve(void)
>  	}
>  }
>  
> +/*
> + * arm_dt_init_cpu_maps - Function retrieves cpu nodes from the device tree
> + * and builds the cpu logical map array containing MPIDR values related to
> + * logical cpus
> + *
> + * Updates the cpu possible mask with the number of parsed cpu nodes
> + */
> +void __init arm_dt_init_cpu_maps(void)
> +{
> +	struct device_node *dn = NULL;
> +	int i, cpu = 1;
> +
> +	while ((dn = of_find_node_by_type(dn, "cpu")) && cpu <= nr_cpu_ids) {

I think all /cpu nodes would have the right type. You could use
for_each_child_of_node here.

> +		const u32 *hwid;
> +		int len;
> +
> +		pr_debug("  * %s...\n", dn->full_name);
> +
> +		hwid = of_get_property(dn, "reg", &len);
> +

Use of_property_read_u32.

> +		if (!hwid || len != 4) {
> +			pr_err("  * %s missing reg property\n", dn->full_name);
> +			continue;
> +		}
> +		/*
> +		 * We want to assign the boot CPU logical id 0.
> +		 * Boot CPU checks its own MPIDR and if matches the current
> +		 * cpu node "reg" value it sets the logical cpu index to 0
> +		 * and stores the physical id accordingly.
> +		 * If MPIDR does not match, assign sequential cpu logical
> +		 * id (starting from 1) and increments it.
> +		 */
> +		i = (be32_to_cpup(hwid) == (read_cpuid_mpidr() & 0xffffff))
> +							? 0 : cpu++;
> +
> +		if (!i)
> +			printk(KERN_INFO "Booting Linux on CPU HWID 0x%x\n",
> +					be32_to_cpup(hwid));
> +
> +		cpu_logical_map(i) = be32_to_cpup(hwid);
> +
> +		set_cpu_possible(i, true);
> +	}
> +}
> +
>  /**
>   * setup_machine_fdt - Machine setup when an dtb was passed to the kernel
>   * @dt_phys: physical address of dt blob
>