mpc85xx: Add cmdline override patch

This patch adds a new kernel option called CONFIG_CMDLINE_OVERRIDE. This
setting is for devices with locked down u-boot environments, where users
are unable to change the default bootargs. When set, the fdt driver will
propagate the cmdline for the kernel from chosen/bootargs-override
instead of chosen/bootargs as long as it exists within the DTB.

Signed-off-by: Chris Blake <chrisrblake93@gmail.com>

target/linux/mpc85xx/config-4.9

@@ -37,6 +37,7 @@ CONFIG_CLONE_BACKWARDS=y
 CONFIG_CLZ_TAB=y
 CONFIG_CMDLINE="console=ttyS0,115200"
 CONFIG_CMDLINE_BOOL=y
+CONFIG_CMDLINE_OVERRIDE=y
 # CONFIG_CORENET_GENERIC is not set
 # CONFIG_CPM2 is not set
 CONFIG_CPU_BIG_ENDIAN=y

target/linux/mpc85xx/patches-4.9/102-powerpc-add-cmdline-override.patch

@@ -0,0 +1,37 @@
+--- a/arch/powerpc/Kconfig
++++ b/arch/powerpc/Kconfig
+@@ -707,6 +707,14 @@ config CMDLINE_FORCE
+ 	  This is useful if you cannot or don't want to change the
+ 	  command-line options your boot loader passes to the kernel.
+ 
++config CMDLINE_OVERRIDE
++	bool "Use alternative cmdline from device tree"
++	help
++	  Some bootloaders may have uneditable bootargs. While CMDLINE_FORCE can
++	  be used, this is not a good option for kernels that are shared across
++	  devices. This setting enables using "chosen/cmdline-override" as the
++	  cmdline if it exists in the device tree.
++
+ config EXTRA_TARGETS
+ 	string "Additional default image types"
+ 	help
+--- a/drivers/of/fdt.c
++++ b/drivers/of/fdt.c
+@@ -1079,6 +1079,17 @@ int __init early_init_dt_scan_chosen(uns
+ 	if (p != NULL && l > 0)
+ 		strlcpy(data, p, min((int)l, COMMAND_LINE_SIZE));
+ 
++	/* CONFIG_CMDLINE_OVERRIDE is used to fallback to a different
++	 * device tree option of chosen/bootargs-override. This is
++	 * helpful on boards where u-boot sets bootargs, and is unable
++	 * to be modified.
++	 */
++#ifdef CONFIG_CMDLINE_OVERRIDE
++	p = of_get_flat_dt_prop(node, "bootargs-override", &l);
++	if (p != NULL && l > 0)
++		strlcpy(data, p, min((int)l, COMMAND_LINE_SIZE));
++#endif
++
+ 	/*
+ 	 * CONFIG_CMDLINE is meant to be a default in case nothing else
+ 	 * managed to set the command line, unless CONFIG_CMDLINE_FORCE