ARC: [cmdline] uboot cmdline handling rework

* Moved cmdline copy from asm to "C" - allows for more robust checking
  of pointer validity etc.

* Remove the Kconfig option to do so, base it on a runtime value passed
  by u-boot
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/Kconfig

@@ -409,17 +409,6 @@ config ARC_DBG_TLB_MISS_COUNT
 	  Counts number of I and D TLB Misses and exports them via Debugfs
 	  The counters can be cleared via Debugfs as well
 
-config CMDLINE_UBOOT
-	bool "Support U-boot kernel command line passing"
-	default n
-	help
-	  If you are using U-boot (www.denx.de) and wish to pass the kernel
-	  command line from the U-boot environment to the Linux kernel then
-	  switch this option on.
-	  ARC U-boot will setup the cmdline in RAM/flash and set r2 to point
-	  to it. kernel startup code will append this to DeviceTree
-	  /bootargs provided cmdline args.
-
 config ARC_BUILTIN_DTB_NAME
 	string "Built in DTB"
 	help

arch/arc/kernel/head.S

@@ -49,25 +49,13 @@ stext:
 	st.ab   0, [r5,4]
 	brlt    r5, r6, 1b
 
-#ifdef CONFIG_CMDLINE_UBOOT
-	; support for bootloader provided cmdline
-	;    If cmdline passed by u-boot, then
-	;    r0 = 1  (because ATAGS parsing, now retired, used to use 0)
-	;    r1 = magic number (board identity)
-	;    r2 = addr of cmdline string (somewhere in memory/flash)
-
-	brne	r0, 1, .Lother_bootup_chores	; u-boot didn't pass cmdline
-	breq	r2, 0, .Lother_bootup_chores	; or cmdline is NULL
-
-	mov	r5, @command_line
-1:
-	ldb.ab  r6, [r2, 1]
-	breq    r6, 0, .Lother_bootup_chores
-	b.d     1b
-	stb.ab  r6, [r5, 1]
-#endif
-
-.Lother_bootup_chores:
+	; Uboot - kernel ABI
+	;    r0 = [0] No uboot interaction, [1] cmdline in r2, [2] DTB in r2
+	;    r1 = magic number (board identity, unused as of now
+	;    r2 = pointer to uboot provided cmdline or external DTB in mem
+	; These are handled later in setup_arch()
+	st	r0, [@uboot_tag]
+	st	r2, [@uboot_arg]
 
 	; Identify if running on ISS vs Silicon
 	; 	IDENTITY Reg [ 3  2  1  0 ]

arch/arc/kernel/setup.c

@@ -29,7 +29,10 @@
 
 int running_on_hw = 1;	/* vs. on ISS */
 
-char __initdata command_line[COMMAND_LINE_SIZE];
+/* Part of U-boot ABI: see head.S */
+int __initdata uboot_tag;
+char __initdata *uboot_arg;
+
 const struct machine_desc *machine_desc;
 
 struct task_struct *_current_task[NR_CPUS];	/* For stack switching */
@@ -311,19 +314,31 @@ void setup_processor(void)
 	arc_chk_fpu();
 }
 
+static inline int is_kernel(unsigned long addr)
+{
+	if (addr >= (unsigned long)_stext && addr <= (unsigned long)_end)
+		return 1;
+	return 0;
+}
+
 void __init setup_arch(char **cmdline_p)
 {
-	/* This also populates @boot_command_line from /bootargs */
-	machine_desc = setup_machine_fdt(__dtb_start);
-	if (!machine_desc)
-		panic("Embedded DT invalid\n");
-
-	/* Append any u-boot provided cmdline */
-#ifdef CONFIG_CMDLINE_UBOOT
-	/* Add a whitespace seperator between the 2 cmdlines */
-	strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
-	strlcat(boot_command_line, command_line, COMMAND_LINE_SIZE);
-#endif
+		machine_desc = setup_machine_fdt(__dtb_start);
+		if (!machine_desc)
+			panic("Embedded DT invalid\n");
+
+		/*
+		 * Append uboot cmdline to embedded DT cmdline.
+		 * setup_machine_fdt() would have populated @boot_command_line
+		 */
+		if (uboot_tag == 1) {
+			BUG_ON(is_kernel(unsigned long)uboot_arg);
+
+			/* Ensure a whitespace between the 2 cmdlines */
+			strlcat(boot_command_line, " ", COMMAND_LINE_SIZE);
+			strlcat(boot_command_line, uboot_arg,
+				COMMAND_LINE_SIZE);
+		}
 
 	/* Save unparsed command line copy for /proc/cmdline */
 	*cmdline_p = boot_command_line;