[PATCH] um: Consolidate MAGIC_SYSRQ into generic Kconfig definition

[Sasha Levin <sashal@kernel.org>]

kconfiglint reports:

  K008: config MAGIC_SYSRQ has prompts in 2 separate definitions

MAGIC_SYSRQ is defined in two places with complementary conditions:

  arch/um/Kconfig:213 — depends on MCONSOLE (UML only)
  lib/Kconfig.debug:665 — depends on !UML (everything except UML)

The UML definition has existed since the initial git import in
commit 1da177e4c3f4 ("Linux-2.6.12-rc2"). UML needs MAGIC_SYSRQ to work
through its mconsole interface rather than through keyboard input, so the
UML version depends on MCONSOLE while the generic version excludes UML
entirely with `depends on !UML`.

These two definitions are logically complementary: on UML, MAGIC_SYSRQ
requires MCONSOLE; on everything else, it has no special dependencies.
This can be expressed as a single definition with
`depends on !UML || MCONSOLE`, which evaluates to:
  - On UML: requires MCONSOLE (same as before)
  - On non-UML: always satisfiable (same as before)

Consolidate into the generic definition in lib/Kconfig.debug by changing
the dependency to `depends on !UML || MCONSOLE` and merging the UML-
specific help text that explains the mconsole-based sysrq interface.
Remove the now-redundant definition from arch/um/Kconfig.

This follows the same unification pattern used by commit 7bd291abe2da
("sched: Unify the SCHED_{SMT,CLUSTER,MC} Kconfig") and our earlier
SCHED_MC consolidation for SH.

No functional change — the resulting Kconfig behavior is identical.

Assisted-by: Claude:claude-opus-4-6 kconfiglint
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/um/Kconfig   | 19 -------------------
 lib/Kconfig.debug | 10 ++++++----
 2 files changed, 6 insertions(+), 23 deletions(-)

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index d9541d13d9eb0..5af245ede463f 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -210,25 +210,6 @@ config MCONSOLE
 
 	  It is safe to say 'Y' here.
 
-config MAGIC_SYSRQ
-	bool "Magic SysRq key"
-	depends on MCONSOLE
-	help
-	  If you say Y here, you will have some control over the system even
-	  if the system crashes for example during kernel debugging (e.g., you
-	  will be able to flush the buffer cache to disk, reboot the system
-	  immediately or dump some status information). A key for each of the
-	  possible requests is provided.
-
-	  This is the feature normally accomplished by pressing a key
-	  while holding SysRq (Alt+PrintScreen).
-
-	  On UML, this is accomplished by sending a "sysrq" command with
-	  mconsole, followed by the letter for the requested command.
-
-	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
-	  unless you really know what this hack does.
-
 config KERNEL_STACK_ORDER
 	int "Kernel stack size order"
 	default 2 if 64BIT
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8ff5adcfe1e0a..695e118f910fb 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -664,7 +664,7 @@ menu "Generic Kernel Debugging Instruments"
 
 config MAGIC_SYSRQ
 	bool "Magic SysRq key"
-	depends on !UML
+	depends on !UML || MCONSOLE
 	help
 	  If you say Y here, you will have some control over the system even
 	  if the system crashes for example during kernel debugging (e.g., you
@@ -672,9 +672,11 @@ config MAGIC_SYSRQ
 	  immediately or dump some status information). This is accomplished
 	  by pressing various keys while holding SysRq (Alt+PrintScreen). It
 	  also works on a serial console (on PC hardware at least), if you
-	  send a BREAK and then within 5 seconds a command keypress. The
-	  keys are documented in <file:Documentation/admin-guide/sysrq.rst>.
-	  Don't say Y unless you really know what this hack does.
+	  send a BREAK and then within 5 seconds a command keypress. On UML,
+	  this is accomplished by sending a "sysrq" command with mconsole,
+	  followed by the letter for the requested command. The keys are
+	  documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say
+	  Y unless you really know what this hack does.
 
 config MAGIC_SYSRQ_DEFAULT_ENABLE
 	hex "Enable magic SysRq key functions by default"
-- 
2.53.0