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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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