Re: [PATCH v3 2/5] ARM: kernel: add device tree init map function

[Nicolas Pitre <nicolas.pitre-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Thu, 15 Nov 2012, 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 device tree HW identifiers are considered valid if all CPU nodes contain
> a "reg" property, there are no duplicate "reg" entries and the DT defines a
> CPU node whose "reg" property matches the MPIDR[23:0] of the boot CPU.
> 
> 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-5wv7dgnIgG8@public.gmane.org>

Acked-by: Nicolas Pitre <nico-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>

> ---
>  Documentation/devicetree/bindings/arm/cpus.txt | 78 ++++++++++++++++++++
>  arch/arm/include/asm/prom.h                    |  2 +
>  arch/arm/kernel/devtree.c                      | 99 ++++++++++++++++++++++++++
>  3 files changed, 179 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..1fab07a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> @@ -0,0 +1,78 @@
> +* 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 properties:
> +
> +- reg:		property matching the CPU MPIDR[23:0] register bits
> +		reg[31:24] bits must be set to 0
> +- compatible:	should be one of:
> +		"arm,arm1020"
> +		"arm,arm1020e"
> +		"arm,arm1022"
> +		"arm,arm1026"
> +		"arm,arm720"
> +		"arm,arm740"
> +		"arm,arm7tdmi"
> +		"arm,arm920"
> +		"arm,arm922"
> +		"arm,arm925"
> +		"arm,arm926"
> +		"arm,arm940"
> +		"arm,arm946"
> +		"arm,arm9tdmi"
> +		"arm,cortex-a5"
> +		"arm,cortex-a7"
> +		"arm,cortex-a8"
> +		"arm,cortex-a9"
> +		"arm,cortex-a15"
> +		"arm,arm1136"
> +		"arm,arm1156"
> +		"arm,arm1176"
> +		"arm,arm11mpcore"
> +		"faraday,fa526"
> +		"intel,sa110"
> +		"intel,sa1100"
> +		"marvell,feroceon"
> +		"marvell,mohawk"
> +		"marvell,xsc3"
> +		"marvell,xscale"
> +
> +Every cpu node is required to set its device_type to "cpu".
> +
> +Example:
> +
> +	cpus {
> +		#size-cells = <0>;
> +		#address-cells = <1>;
> +
> +		CPU0: cpu@0 {
> +			device_type = "cpu";
> +			compatible = <arm, cortex-a15>;
> +			reg = <0x0>;
> +		};
> +
> +		CPU1: cpu@1 {
> +			device_type = "cpu";
> +			compatible = <arm, cortex-a15>;
> +			reg = <0x1>;
> +		};
> +
> +		CPU2: cpu@100 {
> +			device_type = "cpu";
> +			compatible = <arm, cortex-a7>;
> +			reg = <0x100>;
> +		};
> +
> +		CPU3: cpu@101 {
> +			device_type = "cpu";
> +			compatible = <arm, cortex-a7>;
> +			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..cf840b3 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 +63,103 @@ 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)
> +{
> +	/*
> +	 * Temp logical map is initialized with UINT_MAX values that are
> +	 * considered invalid logical map entries since the logical map must
> +	 * contain a list of MPIDR[23:0] values where MPIDR[31:24] must
> +	 * read as 0.
> +	 */
> +	struct device_node *cpu, *cpus;
> +	u32 i, j, cpuidx = 1;
> +	u32 mpidr = is_smp() ? read_cpuid_mpidr() & 0xffffff : 0;
> +	u32 tmp_map[NR_CPUS] = { [0 ... NR_CPUS-1] = UINT_MAX };
> +	bool bootcpu_valid = false;
> +	cpus = of_find_node_by_path("/cpus");
> +
> +	if (!cpus)
> +		return;
> +
> +	for_each_child_of_node(cpus, cpu) {
> +		u32 hwid;
> +
> +		pr_debug(" * %s...\n", cpu->full_name);
> +		/*
> +		 * A device tree containing CPU nodes with missing "reg"
> +		 * properties is considered invalid to build the
> +		 * cpu_logical_map.
> +		 */
> +		if (of_property_read_u32(cpu, "reg", &hwid)) {
> +			pr_debug(" * %s missing reg property\n",
> +				     cpu->full_name);
> +			return;
> +		}
> +
> +		/*
> +		 * 8 MSBs must be set to 0 in the DT since the reg property
> +		 * defines the MPIDR[23:0].
> +		 */
> +		if (hwid & 0xff000000)
> +			return;
> +
> +		/*
> +		 * Duplicate MPIDRs are a recipe for disaster.
> +		 * Scan all initialized entries and check for
> +		 * duplicates. If any is found just bail out.
> +		 * temp values were initialized to UINT_MAX
> +		 * to avoid matching valid MPIDR[23:0] values.
> +		 */
> +		for (j = 0; j < cpuidx; j++)
> +			if (WARN(tmp_map[j] == hwid, "Duplicate /cpu reg "
> +						     "properties in the DT\n"))
> +				return;
> +
> +		/*
> +		 * Build a stashed array of MPIDR values. Numbering scheme
> +		 * requires that if detected the boot CPU must be assigned
> +		 * logical id 0. Other CPUs get sequential indexes starting
> +		 * from 1. If a CPU node with a reg property matching the
> +		 * boot CPU MPIDR is detected, this is recorded so that the
> +		 * logical map built from DT is validated and can be used
> +		 * to override the map created in smp_setup_processor_id().
> +		 */
> +		if (hwid == mpidr) {
> +			i = 0;
> +			bootcpu_valid = true;
> +		} else {
> +			i = cpuidx++;
> +		}
> +
> +		tmp_map[i] = hwid;
> +
> +		if (cpuidx > nr_cpu_ids)
> +			break;
> +	}
> +
> +	if (WARN(!bootcpu_valid, "DT missing boot CPU MPIDR[23:0], "
> +				 "fall back to default cpu_logical_map\n"))
> +		return;
> +
> +	/*
> +	 * Since the boot CPU node contains proper data, and all nodes have
> +	 * a reg property, the DT CPU list can be considered valid and the
> +	 * logical map created in smp_setup_processor_id() can be overridden
> +	 */
> +	for (i = 0; i < cpuidx; i++) {
> +		set_cpu_possible(i, true);
> +		cpu_logical_map(i) = tmp_map[i];
> +		pr_debug("cpu logical map 0x%x\n", cpu_logical_map(i));
> +	}
> +}
> +
>  /**
>   * setup_machine_fdt - Machine setup when an dtb was passed to the kernel
>   * @dt_phys: physical address of dt blob
> -- 
> 1.7.12
> 
>