2 files changed, 79 insertions, 2 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b649c5904a4f..8c9d264f2108 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1960,6 +1960,25 @@ config ARM_ATAG_DTB_COMPAT
           bootloaders, this option allows zImage to extract the information
           from the ATAG list and store it at run time into the appended DTB.
 
+choice
+        prompt "Kernel command line type" if ARM_ATAG_DTB_COMPAT
+        default ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
+
+config ARM_ATAG_DTB_COMPAT_CMDLINE_FROM_BOOTLOADER
+        bool "Use bootloader kernel arguments if available"
+        help
+          Uses the command-line options passed by the boot loader instead of
+          the device tree bootargs property. If the boot loader doesn't provide
+          any, the device tree bootargs property will be used.
+
+config ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND
+        bool "Extend with bootloader kernel arguments"
+        help
+          The command-line arguments provided by the boot loader will be
+          appended to the the device tree bootargs property.
+
+endchoice
+
 config CMDLINE
         string "Default kernel command string"
         default ""
diff --git a/arch/arm/boot/compressed/atags_to_fdt.c b/arch/arm/boot/compressed/atags_to_fdt.c
index 797f04bedb47..aabc02a68482 100644
--- a/arch/arm/boot/compressed/atags_to_fdt.c
+++ b/arch/arm/boot/compressed/atags_to_fdt.c
@@ -1,6 +1,12 @@
 #include <asm/setup.h>
 #include <libfdt.h>
 
+#if defined(CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND)
+#define do_extend_cmdline 1
+#else
+#define do_extend_cmdline 0
+#endif
+
 static int node_offset(void *fdt, const char *node_path)
 {
         int offset = fdt_path_offset(fdt, node_path);
@@ -36,6 +42,48 @@ static int setprop_cell(void *fdt, const char *node_path,
         return fdt_setprop_cell(fdt, offset, property, val);
 }
 
+static const void *getprop(const void *fdt, const char *node_path,
+                           const char *property, int *len)
+{
+        int offset = fdt_path_offset(fdt, node_path);
+
+        if (offset == -FDT_ERR_NOTFOUND)
+                return NULL;
+
+        return fdt_getprop(fdt, offset, property, len);
+}
+
+static void merge_fdt_bootargs(void *fdt, const char *fdt_cmdline)
+{
+        char cmdline[COMMAND_LINE_SIZE];
+        const char *fdt_bootargs;
+        char *ptr = cmdline;
+        int len = 0;
+
+        /* copy the fdt command line into the buffer */
+        fdt_bootargs = getprop(fdt, "/chosen", "bootargs", &len);
+        if (fdt_bootargs)
+                if (len < COMMAND_LINE_SIZE) {
+                        memcpy(ptr, fdt_bootargs, len);
+                        /* len is the length of the string
+                         * including the NULL terminator */
+                        ptr += len - 1;
+                }
+
+        /* and append the ATAG_CMDLINE */
+        if (fdt_cmdline) {
+                len = strlen(fdt_cmdline);
+                if (ptr - cmdline + len + 2 < COMMAND_LINE_SIZE) {
+                        *ptr++ = ' ';
+                        memcpy(ptr, fdt_cmdline, len);
+                        ptr += len;
+                }
+        }
+        *ptr = '\0';
+
+        setprop_string(fdt, "/chosen", "bootargs", cmdline);
+}
+
 /*
  * Convert and fold provided ATAGs into the provided FDT.
  *
@@ -72,8 +120,18 @@ int atags_to_fdt(void *atag_list, void *fdt, int total_space)
 
         for_each_tag(atag, atag_list) {
                 if (atag->hdr.tag == ATAG_CMDLINE) {
-                        setprop_string(fdt, "/chosen", "bootargs",
-                                        atag->u.cmdline.cmdline);
+                        /* Append the ATAGS command line to the device tree
+                         * command line.
+                         * NB: This means that if the same parameter is set in
+                         * the device tree and in the tags, the one from the
+                         * tags will be chosen.
+                         */
+                        if (do_extend_cmdline)
+                                merge_fdt_bootargs(fdt,
+                                                   atag->u.cmdline.cmdline);
+                        else
+                                setprop_string(fdt, "/chosen", "bootargs",
+                                               atag->u.cmdline.cmdline);
                 } else if (atag->hdr.tag == ATAG_MEM) {
                         if (memcount >= sizeof(mem_reg_property)/4)
                                 continue;