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    Subject[PATCH 2/5] of/fdt: add kernel command line option for dtb_compat string
    Date
    From: Dirk Brandewie <dirk.brandewie@gmail.com>

    Adds a kernel command line option "dtb_compat=<string>" and functions
    for architecture/platform specific code to retrieve the command line
    string and locate the compatible DTB linked into the kernel

    of_flat_dt_get_dtb_compatible_string() returns a pointer string passed
    from the command line or a pointer to an empty string.

    of_flat_dt_find_compatible_dtb() returns a pointer to a DTB that is
    compatible with the "compatible" string or a NULL pointer if no
    matching DTB is present.

    Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
    ---
    Documentation/kernel-parameters.txt | 7 +++++
    drivers/of/fdt.c | 52 +++++++++++++++++++++++++++++++++++
    include/linux/of_fdt.h | 4 +++
    3 files changed, 63 insertions(+), 0 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index ed45e98..f9b77fa 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -655,6 +655,13 @@ and is between 256 and 4096 characters. It is defined in the file

    dscc4.setup= [NET]

    + dtb_compat= [KNL]
    + Specify the "compatible" string for the device
    + tree blob present in the kernel image. This
    + string will be used to select the first device
    + tree blob whose compatible property matches
    + the string passed on the kernel commandline.
    +
    dynamic_printk Enables pr_debug()/dev_dbg() calls if
    CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled.
    These can also be switched on/off via
    diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
    index c1360e0..c0858ce 100644
    --- a/drivers/of/fdt.c
    +++ b/drivers/of/fdt.c
    @@ -15,6 +15,8 @@
    #include <linux/of_fdt.h>
    #include <linux/string.h>
    #include <linux/errno.h>
    +#include <asm-generic/vmlinux.lds.h>
    +

    #ifdef CONFIG_PPC
    #include <asm/machdep.h>
    @@ -604,3 +606,53 @@ void __init unflatten_device_tree(void)

    pr_debug(" <- unflatten_device_tree()\n");
    }
    +
    +#define MAX_DTB_COMPAT_STR 64
    +char dtb_compat_name[MAX_DTB_COMPAT_STR] = "";
    +
    +char __init *of_flat_dt_get_dtb_compatible_string(void)
    +{
    + return dtb_compat_name;
    +}
    +
    +
    +extern uint8_t __dtb_start[];
    +extern uint8_t __dtb_end[];
    +void __init *of_flat_dt_find_compatible_dtb(char *name)
    +{
    + void *rc = NULL;
    + unsigned long root, size;
    + struct boot_param_header *orig_initial_boot_params;
    + uint8_t *blob;
    +
    + orig_initial_boot_params = initial_boot_params;
    + blob = __dtb_start;
    + initial_boot_params = (struct boot_param_header *)blob;
    +
    + while (blob < __dtb_end &&
    + (be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER)) {
    + root = of_get_flat_dt_root();
    + if (of_flat_dt_is_compatible(root, name) > 0) {
    + rc = blob;
    + break;
    + }
    +
    + size = be32_to_cpu(initial_boot_params->totalsize);
    + blob = PTR_ALIGN(blob + size, DTB_ALIGNMENT);
    + initial_boot_params = (struct boot_param_header *)blob;
    + }
    +
    + if (rc == NULL)
    + initial_boot_params = orig_initial_boot_params;
    + return rc;
    +}
    +
    +
    +static int __init of_flat_dtb_compat_setup(char *line)
    +{
    + strncpy(dtb_compat_name, line, MAX_DTB_COMPAT_STR);
    + return 1;
    +}
    +
    +early_param("dtb_compat", of_flat_dtb_compat_setup);
    +
    diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
    index 7bbf5b3..29561f4 100644
    --- a/include/linux/of_fdt.h
    +++ b/include/linux/of_fdt.h
    @@ -58,6 +58,7 @@ struct boot_param_header {
    };

    #if defined(CONFIG_OF_FLATTREE)
    +
    /* TBD: Temporary export of fdt globals - remove when code fully merged */
    extern int __initdata dt_root_addr_cells;
    extern int __initdata dt_root_size_cells;
    @@ -82,6 +83,9 @@ extern void early_init_dt_add_memory_arch(u64 base, u64 size);
    extern u64 early_init_dt_alloc_memory_arch(u64 size, u64 align);
    extern u64 dt_mem_next_cell(int s, __be32 **cellp);

    +extern char *of_flat_dt_get_dtb_compatible_string(void);
    +extern void *of_flat_dt_find_compatible_dtb(char *name);
    +
    /*
    * If BLK_DEV_INITRD, the fdt early init code will call this function,
    * to be provided by the arch code. start and end are specified as
    --
    1.7.2.3


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