@@ -1132,6 +1132,22 @@
address must be provided, and the serial port must
already be setup and configured.
+ earlycon_kgdboc= [KGDB,HW]
+ If the boot console provides the ability to read
+ characters and can work in polling mode, you can use
+ this parameter to tell kgdb to use it as a backend
+ until the normal console is registered. Intended to
+ be used together with the kgdboc parameter which
+ specifies the normal console to transition to.
+
+ The the name of the early console should be specified
+ as the value of this parameter. Note that the name of
+ the early console might be different than the tty
+ name passed to kgdboc. If only one boot console with
+ a read() function is enabled it's OK to leave the
+ value blank and the first boot console that implements
+ read() will be picked.
+
earlyprintk= [X86,SH,ARM,M68k,S390]
earlyprintk=vga
earlyprintk=sclp
@@ -1190,6 +1206,10 @@
This is designed to be used in conjunction with
the boot argument: earlyprintk=vga
+ This parameter works in place of the kgdboc parameter
+ but can only be used if the backing tty is available
+ very early in the boot process.
+
edd= [EDD]
Format: {"off" | "on" | "skip[mbr]"}
@@ -274,6 +274,20 @@ don't like this are to hack gdb to send the :kbd:`SysRq-G` for you as well as
on the initial connect, or to use a debugger proxy that allows an
unmodified gdb to do the debugging.
+Kernel parameter: ``earlycon_kgdboc``
+-------------------------------------
+
+If you specify the kernel parameter ``earlycon_kgdboc`` and your serial
+driver registers a boot console that supports polling (doesn't need
+interrupts and implements a nonblocking read() function) kgdb will attempt
+to work using the boot console until it can transition to the regular
+tty driver specified by the ``kgdboc`` parameter.
+
+Normally there is only one boot console (especially that implements the
+read() function) so just adding ``earlycon_kgdboc`` on its own is
+sufficient to make this work. If you have more than one boot console you
+can add the boot console's name to differentiate.
+
Kernel parameter: ``kgdbwait``
------------------------------
The recent patch ("kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles") adds a new kernel command line parameter. Document it. Note that the patch adding the feature does some comparing/contrasting of "earlycon_kgdboc" vs. the existing "ekgdboc". See that patch for more details, but briefly "ekgdboc" can be used _instead_ of "kgdboc" and just makes "kgdboc" do its normal initialization early (only works if your tty driver is already ready). The new "earlycon_kgdboc" works in combination with "kgdboc" and is backed by boot consoles. Signed-off-by: Douglas Anderson <dianders@chromium.org> --- Changes in v2: None .../admin-guide/kernel-parameters.txt | 20 +++++++++++++++++++ Documentation/dev-tools/kgdb.rst | 14 +++++++++++++ 2 files changed, 34 insertions(+)