thunderbolt: Add support for receiver lane margining

USB4 spec defines standard set of registers to be used for receiver lane
margining. This is useful for I/O interface quality and electrical
robustness validation during manufacturing. Expose receiver lane
margining through new debugfs directory "margining" that is added under
each connected USB4 port. Users can then run the margining by writing to
the exposed attributes under that directory.

Signed-off-by: Mika Westerberg <[email protected]>

Author: westeri

drivers/thunderbolt/Kconfig

@@ -27,6 +27,16 @@ config USB4_DEBUGFS_WRITE
 	  Only enable this if you know what you are doing! Never enable
 	  this for production systems or distro kernels.
 
+config USB4_DEBUGFS_MARGINING
+	bool "Expose receiver lane margining operations under USB4 ports (DANGEROUS)"
+	depends on DEBUG_FS
+	depends on USB4_DEBUGFS_WRITE
+	help
+	  Enables hardware and software based receiver lane margining support
+	  under each USB4 port. Used for electrical quality and robustness
+	  validation during manufacturing. Should not be enabled by distro
+	  kernels.
+
 config USB4_KUNIT_TEST
 	bool "KUnit tests" if !KUNIT_ALL_TESTS
 	depends on (USB4=m || KUNIT=y)