driver/ubootdriver: deprecate boot_expression attribute

Checking the U-Boot output for a expression is problematic for cases
where the driver is activated while U-Boot's auto boot is already
interrupted. This is the case if a strategy wants to force() a U-Boot
state.

A similar check happened to be in the BareboxDriver, but it was dropped
in a refactoring [1].

As a first step in harmonizing BareboxDriver and UBootDriver, deprecate
the boot_expression attribute and do not check for it in
_await_prompt() anymore.

[1] 016f605 ("bareboxdriver: refactor login expect loop and add password support")

Signed-off-by: Bastian Krause <bst@pengutronix.de>

CHANGES.rst

@@ -45,6 +45,9 @@ Breaking changes in 0.5.0
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 - ``Config``'s ``get_option()``/``get_target_option()`` convert non-string
   options no longer to strings.
+- `UBootDriver`'s ``boot_expression`` attribute is deprecated, it will no
+  longer check for the string during U-Boot boot. This allows activating the
+  driver on an already running U-Boot.
 
 Known issues in 0.5.0
 ~~~~~~~~~~~~~~~~~~~~~~~~~

doc/configuration.rst

@@ -1447,7 +1447,6 @@ Arguments:
   - init_commands (tuple): optional, tuple of commands to execute after matching the
     prompt
   - password_prompt (str, default="enter Password: "): regex to match the U-Boot password prompt
-  - boot_expression (str, default="U-Boot 20\\d+"): regex to match the U-Boot start string
   - bootstring (str): optional, regex to match on Linux Kernel boot
   - boot_command (str, default="run bootcmd"): boot command for booting target
   - login_timeout (int, default=30): timeout for login prompt detection in seconds
@@ -1498,6 +1497,7 @@ Implements:
      boot_secret: "tpl"
 
 Arguments:
+  - boot_expression (str, default="U-Boot 20\\d+"): regex to match the U-Boot start string
   - boot_secret (str, default="a"): secret used to unlock prompt
   - login_timeout (int, default=60): timeout for password/login prompt detection
   - for other arguments, see `UBootDriver`_

labgrid/driver/smallubootdriver.py

@@ -46,6 +46,7 @@ class SmallUBootDriver(UBootDriver):
         login_timeout (int): optional, timeout for login prompt detection,
     """
 
+    boot_expression = attr.ib(default=r"U-Boot 20\d+", validator=attr.validators.instance_of(str))
     boot_secret = attr.ib(default="a", validator=attr.validators.instance_of(str))
     boot_secret_nolf = attr.ib(default=False, validator=attr.validators.instance_of(bool))
     login_timeout = attr.ib(default=60, validator=attr.validators.instance_of(int))

labgrid/driver/ubootdriver.py

@@ -27,7 +27,7 @@ class UBootDriver(CommandMixin, Driver, CommandProtocol, LinuxBootProtocol):
         autoboot (str): optional, string to search for to interrupt autoboot
         interrupt (str): optional, character to interrupt autoboot and go to prompt
         password_prompt (str): optional, string to detect the password prompt
-        boot_expression (str): optional, string to search for on U-Boot start
+        boot_expression (str): optional, deprecated
         bootstring (str): optional, string that indicates that the Kernel is booting
         boot_command (str): optional boot command to boot target
         login_timeout (int): optional, timeout for login prompt detection
@@ -41,7 +41,7 @@ class UBootDriver(CommandMixin, Driver, CommandProtocol, LinuxBootProtocol):
     interrupt = attr.ib(default="\n", validator=attr.validators.instance_of(str))
     init_commands = attr.ib(default=attr.Factory(tuple), converter=tuple)
     password_prompt = attr.ib(default="enter Password:", validator=attr.validators.instance_of(str))
-    boot_expression = attr.ib(default=r"U-Boot 20\d+", validator=attr.validators.instance_of(str))
+    boot_expression = attr.ib(default="", validator=attr.validators.instance_of(str))
     bootstring = attr.ib(default=r"Linux version \d", validator=attr.validators.instance_of(str))
     boot_command = attr.ib(default="run bootcmd", validator=attr.validators.instance_of(str))
     login_timeout = attr.ib(default=30, validator=attr.validators.instance_of(int))
@@ -55,6 +55,10 @@ def __attrs_post_init__(self):
         self.logger = logging.getLogger(f"{self}:{self.target}")
         self._status = 0
 
+        if self.boot_expression:
+            import warnings
+            warnings.warn("boot_expression is deprecated and will be ignored", DeprecationWarning)
+
     def on_activate(self):
         """Activate the UBootDriver
 
@@ -146,7 +150,6 @@ def _await_prompt(self):
         """Await autoboot line and stop it to get to the prompt, optionally
         enter the password.
         """
-        self.console.expect(self.boot_expression, timeout=self.login_timeout)
         while True:
             index, _, _, _ = self.console.expect(
                 [self.prompt, self.autoboot, self.password_prompt]