kgdboc: Add ekgdboc for early use of the kernel debugger

The ekgdboc= differs from kgdboc= in that you can begin debuggin as
soon as the exceptions are setup and the kgdb I/O driver is available,
instead of waiting until the tty subsystem is available.

CC: kgdb-bugreport@lists.sourceforge.net
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

2 files changed, 25 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index bdce359820bb..4c44d01c67f4 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -713,6 +713,12 @@ and is between 256 and 4096 characters. It is defined in the file
                         The VGA output is eventually overwritten by the real
                         console.
 
+        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
+                        ekgdboc=kbd
+
+                        This is desgined to be used in conjunction with
+                        the boot argument: earlyprintk=vga
+
         eata=           [HW,SCSI]
 
         edd=            [EDD]
diff --git a/drivers/serial/kgdboc.c b/drivers/serial/kgdboc.c
index b765ab48dfe7..a9a94ae72349 100644
--- a/drivers/serial/kgdboc.c
+++ b/drivers/serial/kgdboc.c
@@ -223,6 +223,25 @@ static struct kgdb_io kgdboc_io_ops = {
         .post_exception         = kgdboc_post_exp_handler,
 };
 
+#ifdef CONFIG_KGDB_SERIAL_CONSOLE
+/* This is only available if kgdboc is a built in for early debugging */
+int __init kgdboc_early_init(char *opt)
+{
+        /* save the first character of the config string because the
+         * init routine can destroy it.
+         */
+        char save_ch;
+
+        kgdboc_option_setup(opt);
+        save_ch = config[0];
+        init_kgdboc();
+        config[0] = save_ch;
+        return 0;
+}
+
+early_param("ekgdboc", kgdboc_early_init);
+#endif /* CONFIG_KGDB_SERIAL_CONSOLE */
+
 module_init(init_kgdboc);
 module_exit(cleanup_kgdboc);
 module_param_call(kgdboc, param_set_kgdboc_var, param_get_string, &kps, 0644);