[PATCH] RISC-V: Implement built-in command line feature

[mick@ics.forth.gr (Nick Kossifidis)]

This patch enables the use of a built-in kernel command line, which can
optionaly also override the command line provided by the boot loader.

Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
---
 arch/riscv/kernel/setup.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index aee603123..fd171ca7f 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -30,6 +30,7 @@
 #include <linux/of_platform.h>
 #include <linux/sched/task.h>
 #include <linux/swiotlb.h>
+#include <linux/string.h>
 
 #include <asm/setup.h>
 #include <asm/sections.h>
@@ -39,6 +40,14 @@
 #include <asm/tlbflush.h>
 #include <asm/thread_info.h>
 
+#ifdef CONFIG_CMDLINE_BOOL
+#ifdef CONFIG_CMDLINE_FORCE
+	static const char fixed_cmdline[] __initconst = CONFIG_CMDLINE;
+#else
+	static char builtin_cmdline[] __initdata = CONFIG_CMDLINE;
+#endif
+#endif
+
 #ifdef CONFIG_EARLY_PRINTK
 static void sbi_console_write(struct console *co, const char *buf,
 			      unsigned int n)
@@ -215,6 +224,46 @@ void __init setup_arch(char **cmdline_p)
                register_console(early_console);
        }
 #endif
+
+	/* When we return, cmdline_p should point to a temporary
+	 * buffer on the kernel's init section (that gets cleaned up
+	 * later on) to be saved on static_command_line and parsed for
+	 * parameters.
+	 *
+	 * That string may get tweaked during parameter parsing so we
+	 * also want to keep an untouched version of the command line
+	 * to display on dmesg, /proc/cmdline etc.
+	 *
+	 * At this point boot_command_line is a temporary buffer
+	 * (also on the init section) that contains the command line
+	 * string passed from the boot loader. After we return,
+	 * it will be saved to saved_command_line that holds the
+	 * untouched version of the command line.
+	 *
+	 * Since we won't be doing any parameter parsing here, we'll
+	 * hold the initial/untouched command line string on
+	 * boot_command_line and make cmdline_p point to it as well.
+	 * This way boot_command_line will be copied to both
+	 * saved_command_line and static_command_line.
+	 */
+#ifdef CONFIG_CMDLINE_BOOL
+#ifdef CONFIG_CMDLINE_FORCE
+	/* Built-in args override boot loader args and
+	 * boot loader args are being ignored.
+	 */
+	strlcpy(boot_command_line, fixed_cmdline, COMMAND_LINE_SIZE);
+#else
+	/* Boot loader args override built-in args so we
+	 * need to put built-in args before boot loader args.
+	 */
+	if (builtin_cmdline[0]) {
+		strlcat(builtin_cmdline, " ", COMMAND_LINE_SIZE);
+		strlcat(builtin_cmdline, boot_command_line, COMMAND_LINE_SIZE);
+		strlcpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
+	}
+#endif
+#endif
+
 	*cmdline_p = boot_command_line;
 
 	parse_early_param();
-- 
2.16.4