kernel: add find and replace bootargs hack

Add find and replace bootargs to device tree cmdline hack. Now we can
find and replace bootargs by setting bootargs-find-1, bootargs-replace-1
and bootargs-find-2, bootargs-replace-2 under the chosen node in the
device tree.

This hack was implemented to support Linksys MX4300, a dual firmware
device. This device's default kernel command line isn't compatiailbe
with OpenWrt's UBI, so we leverage find and replace to dynamically
patch the command line while keeping the partition to boot set by u-boot.

Signed-off-by: Qiyuan Zhang <[email protected]>

target/linux/generic/hack-6.6/920-device_tree_cmdline.patch

@@ -9,13 +9,78 @@ Subject: [PATCH] of/ftd: add device tree cmdline
 
 --- a/drivers/of/fdt.c
 +++ b/drivers/of/fdt.c
-@@ -1185,6 +1185,9 @@ int __init early_init_dt_scan_chosen(cha
- 	p = of_get_flat_dt_prop(node, "bootargs", &l);
+@@ -1157,6 +1157,16 @@ int __init early_init_dt_scan_chosen(cha
+ 	const void *rng_seed;
+ 	const void *fdt = initial_boot_params;
+
++	int i, cmd_len, f_len, r_len;
++	char *s_ptr, *l_end, *r_end, *cur_ptr, *end_ptr;
++	int  offset, step;
++
++	const int bootargs_replace_num = 2;
++	const char *bootargs_replace_nodes[2][2] =
++            { {"bootargs-find-1", "bootargs-replace-1"},
++              {"bootargs-find-2", "bootargs-replace-2"} };
++
++
+ 	node = fdt_path_offset(fdt, "/chosen");
+ 	if (node < 0)
+ 		node = fdt_path_offset(fdt, "/chosen@0");
+@@ -1186,6 +1196,57 @@ int __init early_init_dt_scan_chosen(cha
  	if (p != NULL && l > 0)
  		strscpy(cmdline, p, min(l, COMMAND_LINE_SIZE));
+
++	for(i = 0; i < bootargs_replace_num; i++) {
++		p = of_get_flat_dt_prop(node, bootargs_replace_nodes[i][0], &f_len);
++		if (p != NULL && f_len > 0 && (s_ptr = strstr(cmdline, p))) {
++			p = of_get_flat_dt_prop(node, bootargs_replace_nodes[i][1], &r_len);
++			if (p != NULL && f_len > 0) {
++				p = of_get_flat_dt_prop(node, bootargs_replace_nodes[i][1], &r_len);
++
++				if (p != NULL && r_len > 0) {
++					pr_info("Input kernel commad line: %s\n", cmdline);
++
++					cmd_len = strlen(cmdline);
++
++					if (cmd_len - f_len + r_len < COMMAND_LINE_SIZE) {
++
++						pr_info("Replace kernel command line with %s\n", bootargs_replace_nodes[i][1]);
++
++						offset = r_len - f_len;
++
++						if (offset != 0) {
++							l_end = s_ptr + f_len -	1;
++							r_end = cmdline + cmd_len;
++
++							if (offset > 0) {
++								step = -1;
++								cur_ptr = r_end;
++								end_ptr = l_end + step;
++							} else {
++								step = 1;
++								cur_ptr = l_end;
++								end_ptr = r_end + step;
++							}
++
++							for (; cur_ptr != end_ptr; cur_ptr += step) {
++								*(cur_ptr + offset) = *cur_ptr;
++							}
++						}
++
++						strncpy(s_ptr, p, r_len - 1);
++
++						pr_info("Kernel command line after replacement: %s\n", cmdline);
++					} else {
++						pr_err("Replace kernel command line with %s failed\n", bootargs_replace_nodes[i][1]);
++					}
++				}
++			}
++		}
++	}
 +	p = of_get_flat_dt_prop(node, "bootargs-append", &l);
 +	if (p != NULL && l > 0)
 +		strlcat(cmdline, p, min_t(int, strlen(cmdline) + (int)l, COMMAND_LINE_SIZE));
- 
++
  handle_cmdline:
  	/*
+ 	 * CONFIG_CMDLINE is meant to be a default in case nothing else

target/linux/qualcommax/files/arch/arm64/boot/dts/qcom/ipq8174-mx4300.dts

@@ -7,6 +7,15 @@
 / {
 	model = "Linksys MX4300";
 	compatible = "linksys,mx4300", "qcom,ipq8074";
+
+	chosen {
+		bootargs-append = "";
+		// Replace the bootargs from u-boot with find and replace
+		bootargs-find-1 = "init=/sbin/init rootfstype=squashfs ubi.mtd=22,2048 ubi.block=0,0 root=/dev/ubiblock0_0 rootwait ro";
+		bootargs-find-2 = "init=/sbin/init rootfstype=squashfs ubi.mtd=24,2048 ubi.block=0,0 root=/dev/ubiblock0_0 rootwait ro";
+		bootargs-replace-1 = "rootfstype=squashfs ubi.mtd=22,4096 ubi.block=0,0 root=/dev/ubiblock0_0 rootwait ro";
+		bootargs-replace-2 = "rootfstype=squashfs ubi.mtd=24,4096 ubi.block=0,0 root=/dev/ubiblock0_0 rootwait ro";
+	};
 };
 
 &qpic_nand {