MIPS: Fix and enhance built-in kernel command line

Currently, MIPS kernels silently overwrite kernel command-line parameters
hardcoded in CONFIG_CMDLINE by the ones received from firmware.  Therefore,
using firmware remains the only reliable method to transfer the
command-line parameters, which is not always desirable or convenient, and
the CONFIG_CMDLINE option is thereby effectively rendered useless.

This patch fixes the problem described above and introduces a more flexible
scheme of handling the kernel command line, in a manner identical to what is
currently used for x86.  The default behavior, i.e. when CONFIG_CMDLINE_BOOL
is not defined, retains the existing semantics, and firmware command-line
arguments override the hardcoded ones.

[Ralf: I fixed up all the defconfig files so the stay unaffected by this
change.]

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/689/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 41 insertions, 4 deletions

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 23817bc7a26a..d2b88a0be519 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -20,15 +20,52 @@ config EARLY_PRINTK
           doesn't cooperate with an X server. You should normally say N here,
           unless you want to debug such a crash.
 
+config CMDLINE_BOOL
+        bool "Built-in kernel command line"
+        default n
+        help
+          For most systems, it is firmware or second stage bootloader that
+          by default specifies the kernel command line options.  However,
+          it might be necessary or advantageous to either override the
+          default kernel command line or add a few extra options to it.
+          For such cases, this option allows you to hardcode your own
+          command line options directly into the kernel.  For that, you
+          should choose 'Y' here, and fill in the extra boot arguments
+          in CONFIG_CMDLINE.
+
+          The built-in options will be concatenated to the default command
+          line if CMDLINE_OVERRIDE is set to 'N'. Otherwise, the default
+          command line will be ignored and replaced by the built-in string.
+
+          Most MIPS systems will normally expect 'N' here and rely upon
+          the command line from the firmware or the second-stage bootloader.
+
 config CMDLINE
         string "Default kernel command string"
+        depends on CMDLINE_BOOL
         default ""
         help
           On some platforms, there is currently no way for the boot loader to
-          pass arguments to the kernel. For these platforms, you can supply
-          some command-line options at build time by entering them here.  In
-          other cases you can specify kernel args so that you don't have
-          to set them up in board prom initialization routines.
+          pass arguments to the kernel.  For these platforms, and for the cases
+          when you want to add some extra options to the command line or ignore
+          the default command line, you can supply some command-line options at
+          build time by entering them here.  In other cases you can specify
+          kernel args so that you don't have to set them up in board prom
+          initialization routines.
+
+          For more information, see the CMDLINE_BOOL and CMDLINE_OVERRIDE
+          options.
+
+config CMDLINE_OVERRIDE
+        bool "Built-in command line overrides firware arguments"
+        default n
+        depends on CMDLINE_BOOL
+        help
+          By setting this option to 'Y' you will have your kernel ignore
+          command line arguments from firmware or second stage bootloader.
+          Instead, the built-in command line will be used exclusively.
+
+          Normally, you will choose 'N' here.
 
 config DEBUG_STACK_USAGE
         bool "Enable stack utilization instrumentation"