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    Subject[PATCH] 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>". This string
    will be used to select the first compatible device tree blob linked
    into the kernel if a device tree blob is was *not* passed in by the
    bootloader.

    Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
    ---
    Documentation/kernel-parameters.txt | 8 ++++++
    drivers/of/fdt.c | 48 +++++++++++++++++++++++++++++++++++
    2 files changed, 56 insertions(+), 0 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index 92e83e5..64093e5 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -655,6 +655,14 @@ 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 vmlinux image. This
    + string will be used to select the first device
    + tree blob whose compatible property matches
    + the string if a dtb was NOT passed in by the
    + bootloader.
    +
    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..ca1318c 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 +606,49 @@ void __init unflatten_device_tree(void)

    pr_debug(" <- unflatten_device_tree()\n");
    }
    +
    +extern uint8_t __dtb_start[];
    +extern uint8_t __dtb_end[];
    +static 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) {
    + if (be32_to_cpu(initial_boot_params->magic) != OF_DT_HEADER) {
    + WARN(1, "Invalid device tree blob in vmlinux\n");
    + break;
    + }
    +
    + 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, STRUCT_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)
    +{
    + if (!initial_boot_params)
    + initial_boot_params = of_flat_dt_find_compatible_dtb(line);
    + return 1;
    +}
    +
    +early_param("dtb_compat", of_flat_dtb_compat_setup);
    +
    --
    1.7.2.3


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