Clarify docs: Add example for dtmerge and more precisely describe available parameters

Author: Torben Woltjen

dtmerge/README.md

@@ -21,9 +21,9 @@ Install the prerequisites with "sudo apt install cmake libfdt-dev" - you need at
 ```
 Usage:
     dtmerge [<options] <base dtb> <merged dtb> - [param=value] ...
-        to apply a parameter to the base dtb (like dtparam)
+        to apply a parameter to the base dtb, without an overlay (like dtparam)
     dtmerge [<options] <base dtb> <merged dtb> <overlay dtb> [param=value] ...
-        to apply an overlay with parameters (like dtoverlay)
+        to apply an overlay, optionally with parameters (like dtoverlay)
   where <options> is any of:
     -d      Enable debug output
     -h      Show this help message

dtmerge/dtmerge.1

@@ -52,13 +52,18 @@ Displays help on the application.
 .TP
 .B dtmerge /boot/bcm2711-rpi-4-b.dtb out.dtb - spi=on i2c=on
 Produce a device-tree for the Raspberry Pi 4 in "out.dtb" which has the SPI and
-I2C interfaces activated.
+I2C interfaces activated. No additional device-tree overlay is applied.
 .
 .TP
 .B dtmerge /boot/bcm2710-rpi-3-b-plus.dtb out.dtb /boot/overlays/gpio-shutdown.dtbo
 Produce a device-tree for the Raspberry Pi 3+ in "out.dtb" which includes the
 GPIO shutdown overlay (with all parameters set to their default).
 .
+.TP
+.B dtmerge /boot/bcm2710-rpi-3-b-plus.dtb out.dtb /boot/overlays/gpio-shutdown.dtbo gpio_pin=5
+Produce a device-tree for the Raspberry Pi 3+ in "out.dtb" which includes the
+GPIO shutdown overlay. Additionally, it sets the gpio shutdown pin to 5.
+.
 .
 .SH SEE ALSO
 .BR dtoverlay (1),

dtmerge/dtmerge.c

@@ -35,9 +35,9 @@ static void usage(void)
 {
     printf("Usage:\n");
     printf("    dtmerge [<options] <base dtb> <merged dtb> - [param=value] ...\n");
-    printf("        to apply a parameter to the base dtb (like dtparam)\n");
+    printf("        to apply a parameter to the base dtb, without an overlay (like dtparam)\n");
     printf("    dtmerge [<options] <base dtb> <merged dtb> <overlay dtb> [param=value] ...\n");
-    printf("        to apply an overlay with parameters (like dtoverlay)\n");
+    printf("        to apply an overlay, optionally with parameters (like dtoverlay)\n");
     printf("  where <options> is any of:\n");
     printf("    -d      Enable debug output\n");
     printf("    -h      Show this help message\n");