[PATCH] of/fdt: add kernel command line option for dtb_compat string

[dirk.brandewie at gmail.com]

From: Dirk Brandewie <dirk.brandewie at 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 at 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