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 <[email protected]>
> ---
> 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@0 {
> + device_type = "cpu";
> + reg = <0x0>;
> + };
> +
> + CPU1: cpu@1 {
> + device_type = "cpu";
> + reg = <0x1>;
> + };
> +
> + CPU2: cpu@100 {
> + device_type = "cpu";
> + reg = <0x100>;
> + };
> +
> + CPU3: cpu@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
>
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