9 files changed, 56 insertions, 24 deletions
diff --git a/docs/cli_commands.md b/docs/cli_commands.md
index c7468eb5e7..8fa7ad41dc 100644
--- a/docs/cli_commands.md
+++ b/docs/cli_commands.md
@@ -17,7 +17,7 @@ qmk compile [-c] <configuratorExport.json>
 **Usage for Keymaps**:
 
 ```
-qmk compile [-c] [-e <var>=<value>] -kb <keyboard_name> -km <keymap_name>
+qmk compile [-c] [-e <var>=<value>] [-j <num_jobs>] -kb <keyboard_name> -km <keymap_name>
 ```
 
 **Usage in Keyboard Directory**:  
@@ -73,6 +73,17 @@ $ qmk compile -kb dz60
 ...
 ```
 
+**Parallel Compilation**:
+
+It is possible to speed up compilation by adding the `-j`/`--parallel` flag.
+```
+qmk compile -j <num_jobs> -kb <keyboard_name>
+```
+The `num_jobs` argument determines the maximum number of jobs that can be used. Setting it to zero will enable parallel compilation without limiting the maximum number of jobs.
+```
+qmk compile -j 0 -kb <keyboard_name>
+```
+
 ## `qmk flash`
 
 This command is similar to `qmk compile`, but can also target a bootloader. The bootloader is optional, and is set to `:flash` by default. To specify a different bootloader, use `-bl <bootloader>`. Visit the [Flashing Firmware](flashing.md) guide for more details of the available bootloaders.
@@ -82,13 +93,13 @@ This command is directory aware. It will automatically fill in KEYBOARD and/or K
 **Usage for Configurator Exports**:
 
 ```
-qmk flash [-bl <bootloader>] [-c] [-e <var>=<value>] <configuratorExport.json>
+qmk flash [-bl <bootloader>] [-c] [-e <var>=<value>] [-j <num_jobs>] <configuratorExport.json>
 ```
 
 **Usage for Keymaps**:
 
 ```
-qmk flash -kb <keyboard_name> -km <keymap_name> [-bl <bootloader>] [-c] [-e <var>=<value>]
+qmk flash -kb <keyboard_name> -km <keymap_name> [-bl <bootloader>] [-c] [-e <var>=<value>] [-j <num_jobs>]
 ```
 
 **Listing the Bootloaders**
diff --git a/lib/python/qmk/cli/compile.py b/lib/python/qmk/cli/compile.py
index 7a45e77214..acbd778649 100755
--- a/lib/python/qmk/cli/compile.py
+++ b/lib/python/qmk/cli/compile.py
@@ -18,7 +18,7 @@ from qmk.keymap import keymap_completer
 @cli.argument('-kb', '--keyboard', type=keyboard_folder, completer=keyboard_completer, help='The keyboard to build a firmware for. Ignored when a configurator export is supplied.')
 @cli.argument('-km', '--keymap', completer=keymap_completer, help='The keymap to build a firmware for. Ignored when a configurator export is supplied.')
 @cli.argument('-n', '--dry-run', arg_only=True, action='store_true', help="Don't actually build, just show the make command to be run.")
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-e', '--env', arg_only=True, action='append', default=[], help="Set a variable to be passed to make. May be passed multiple times.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.subcommand('Compile a QMK Firmware.')
diff --git a/lib/python/qmk/cli/flash.py b/lib/python/qmk/cli/flash.py
index 1b2932a5b2..c2d9e09c69 100644
--- a/lib/python/qmk/cli/flash.py
+++ b/lib/python/qmk/cli/flash.py
@@ -38,7 +38,7 @@ def print_bootloader_help():
 @cli.argument('-km', '--keymap', help='The keymap to build a firmware for. Use this if you dont have a configurator file. Ignored when a configurator file is supplied.')
 @cli.argument('-kb', '--keyboard', type=keyboard_folder, completer=keyboard_completer, help='The keyboard to build a firmware for. Use this if you dont have a configurator file. Ignored when a configurator file is supplied.')
 @cli.argument('-n', '--dry-run', arg_only=True, action='store_true', help="Don't actually build, just show the make command to be run.")
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-e', '--env', arg_only=True, action='append', default=[], help="Set a variable to be passed to make. May be passed multiple times.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.subcommand('QMK Flash.')
diff --git a/lib/python/qmk/cli/multibuild.py b/lib/python/qmk/cli/multibuild.py
index bdb0b493c8..85ed0fa1e9 100755
--- a/lib/python/qmk/cli/multibuild.py
+++ b/lib/python/qmk/cli/multibuild.py
@@ -10,7 +10,7 @@ from subprocess import DEVNULL
 from milc import cli
 
 from qmk.constants import QMK_FIRMWARE
-from qmk.commands import _find_make
+from qmk.commands import _find_make, get_make_parallel_args
 import qmk.keyboard
 import qmk.keymap
 
@@ -28,7 +28,7 @@ def _is_split(keyboard_name):
     return True if 'SPLIT_KEYBOARD' in rules_mk and rules_mk['SPLIT_KEYBOARD'].lower() == 'yes' else False
 
 
-@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs to run.")
+@cli.argument('-j', '--parallel', type=int, default=1, help="Set the number of parallel make jobs; 0 means unlimited.")
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.argument('-f', '--filter', arg_only=True, action='append', default=[], help="Filter the list of keyboards based on the supplied value in rules.mk. Supported format is 'SPLIT_KEYBOARD=yes'. May be passed multiple times.")
 @cli.argument('-km', '--keymap', type=str, default='default', help="The keymap name to build. Default is 'default'.")
@@ -80,7 +80,7 @@ all: {keyboard_safe}_binary
                 )
                 # yapf: enable
 
-    cli.run([make_cmd, '-j', str(cli.args.parallel), '-f', makefile.as_posix(), 'all'], capture_output=False, stdin=DEVNULL)
+    cli.run([make_cmd, *get_make_parallel_args(cli.args.parallel), '-f', makefile.as_posix(), 'all'], capture_output=False, stdin=DEVNULL)
 
     # Check for failures
     failures = [f for f in builddir.glob(f'failed.log.{os.getpid()}.*')]
diff --git a/lib/python/qmk/commands.py b/lib/python/qmk/commands.py
index 8c66228b2b..421453d837 100644
--- a/lib/python/qmk/commands.py
+++ b/lib/python/qmk/commands.py
@@ -52,7 +52,7 @@ def create_make_target(target, parallel=1, **env_vars):
     for key, value in env_vars.items():
         env.append(f'{key}={value}')
 
-    return [make_cmd, '-j', str(parallel), *env, target]
+    return [make_cmd, *get_make_parallel_args(parallel), *env, target]
 
 
 def create_make_command(keyboard, keymap, target=None, parallel=1, **env_vars):
@@ -112,6 +112,24 @@ def get_git_version(current_time, repo_dir='.', check_dir='.'):
     return current_time
 
 
+def get_make_parallel_args(parallel=1):
+    """Returns the arguments for running the specified number of parallel jobs.
+    """
+    parallel_args = []
+
+    if int(parallel) <= 0:
+        # 0 or -1 means -j without argument (unlimited jobs)
+        parallel_args.append('--jobs')
+    else:
+        parallel_args.append('--jobs=' + str(parallel))
+
+    if int(parallel) != 1:
+        # If more than 1 job is used, synchronize parallel output by target
+        parallel_args.append('--output-sync=target')
+
+    return parallel_args
+
+
 def create_version_h(skip_git=False, skip_all=False):
     """Generate version.h contents
     """
@@ -185,8 +203,7 @@ def compile_configurator_json(user_keymap, bootloader=None, parallel=1, **env_va
         make_command.append('-s')
 
     make_command.extend([
-        '-j',
-        str(parallel),
+        *get_make_parallel_args(parallel),
         '-r',
         '-R',
         '-f',
diff --git a/message.mk b/message.mk
index dcd47e5501..419e3f5f31 100644
--- a/message.mk
+++ b/message.mk
@@ -36,6 +36,10 @@ PRINT_OK = $(SILENT) || printf " $(OK_STRING)" | $(AWK_STATUS)
 BUILD_CMD = LOG=$$($(CMD) 2>&1) ; if [ $$? -gt 0 ]; then $(PRINT_ERROR); elif [ "$$LOG" != "" ] ; then $(PRINT_WARNING); else $(PRINT_OK); fi;
 MAKE_MSG_FORMAT = $(AWK) '{ printf "%-118s", $$0;}'
 
+# The UNSYNC_OUTPUT_CMD command disables the `--output-sync` for the current command, if the `--output-sync` granularity is `target` or lower.
+# This is achieved by telling make to treat the current command as if it invokes a recursive make subcommand (as if by calling `$(MAKE)`).
+UNSYNC_OUTPUT_CMD = +true
+
 # Define Messages
 # English
 MSG_ERRORS_NONE = Errors: none
diff --git a/platforms/arm_atsam/flash.mk b/platforms/arm_atsam/flash.mk
index 444ba77f53..f31d4b4d95 100644
--- a/platforms/arm_atsam/flash.mk
+++ b/platforms/arm_atsam/flash.mk
@@ -5,7 +5,7 @@
 
 flash: bin
 ifneq ($(strip $(PROGRAM_CMD)),)
-	$(PROGRAM_CMD)
+	$(UNSYNC_OUTPUT_CMD) && $(PROGRAM_CMD)
 else
 	$(PRINT_OK); $(SILENT) || printf "$(MSG_FLASH_ARCH)"
 endif
diff --git a/platforms/avr/flash.mk b/platforms/avr/flash.mk
index e679bf0ace..8eef5fbb03 100644
--- a/platforms/avr/flash.mk
+++ b/platforms/avr/flash.mk
@@ -161,19 +161,19 @@ hid_bootloader: $(BUILD_DIR)/$(TARGET).hex check-size cpfirmware
 
 flash:  $(BUILD_DIR)/$(TARGET).hex check-size cpfirmware
 ifneq ($(strip $(PROGRAM_CMD)),)
-	$(PROGRAM_CMD)
+	$(UNSYNC_OUTPUT_CMD) && $(PROGRAM_CMD)
 else ifeq ($(strip $(BOOTLOADER)), caterina)
-	$(call EXEC_AVRDUDE)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_AVRDUDE)
 else ifeq ($(strip $(BOOTLOADER)), halfkay)
-	$(call EXEC_TEENSY)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_TEENSY)
 else ifeq (dfu,$(findstring dfu,$(BOOTLOADER)))
-	$(call EXEC_DFU)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_DFU)
 else ifeq ($(strip $(BOOTLOADER)), USBasp)
-	$(call EXEC_USBASP)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_USBASP)
 else ifeq ($(strip $(BOOTLOADER)), bootloadHID)
-	$(call EXEC_BOOTLOADHID)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_BOOTLOADHID)
 else ifeq ($(strip $(BOOTLOADER)), qmk-hid)
-	$(call EXEC_HID_LUFA)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_HID_LUFA)
 else
 	$(PRINT_OK); $(SILENT) || printf "$(MSG_FLASH_BOOTLOADER)"
 endif
diff --git a/platforms/chibios/flash.mk b/platforms/chibios/flash.mk
index 46aff6e4b0..c0b32c2f2b 100644
--- a/platforms/chibios/flash.mk
+++ b/platforms/chibios/flash.mk
@@ -73,15 +73,15 @@ teensy: $(BUILD_DIR)/$(TARGET).hex cpfirmware sizeafter
 
 flash: $(BUILD_DIR)/$(TARGET).bin cpfirmware sizeafter
 ifneq ($(strip $(PROGRAM_CMD)),)
-	$(PROGRAM_CMD)
+	$(UNSYNC_OUTPUT_CMD) && $(PROGRAM_CMD)
 else ifeq ($(strip $(BOOTLOADER)),kiibohd)
-	$(call EXEC_DFU_UTIL)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_DFU_UTIL)
 else ifeq ($(strip $(MCU_FAMILY)),KINETIS)
-	$(call EXEC_TEENSY)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_TEENSY)
 else ifeq ($(strip $(MCU_FAMILY)),MIMXRT1062)
-	$(call EXEC_TEENSY)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_TEENSY)
 else ifeq ($(strip $(MCU_FAMILY)),STM32)
-	$(call EXEC_DFU_UTIL)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_DFU_UTIL)
 else
 	$(PRINT_OK); $(SILENT) || printf "$(MSG_FLASH_BOOTLOADER)"
 endif