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From: Douglas Anderson <dianders@chromium.org>
To: jason.wessel@windriver.com, daniel.thompson@linaro.org,
	gregkh@linuxfoundation.org
Cc: kgdb-bugreport@lists.sourceforge.net, mingo@redhat.com,
	hpa@zytor.com, bp@alien8.de, linux-serial@vger.kernel.org,
	agross@kernel.org, tglx@linutronix.de, frowand.list@gmail.com,
	bjorn.andersson@linaro.org, jslaby@suse.com,
	catalin.marinas@arm.com, corbet@lwn.net, will@kernel.org,
	Douglas Anderson <dianders@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@suse.de>, Juergen Gross <jgross@suse.com>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter
Date: Tue, 21 Apr 2020 14:14:45 -0700	[thread overview]
Message-ID: <20200421141234.v2.7.I7d5eb42c6180c831d47aef1af44d0b8be3fac559@changeid> (raw)
In-Reply-To: <20200421211447.193860-1-dianders@chromium.org>

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(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f2a93c8679e8..588625ec2993 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -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]"}
 
diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst
index d38be58f872a..c0b321403d9a 100644
--- a/Documentation/dev-tools/kgdb.rst
+++ b/Documentation/dev-tools/kgdb.rst
@@ -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``
 ------------------------------
 
-- 
2.26.1.301.g55bc3eb7cb9-goog


  parent reply	other threads:[~2020-04-21 21:15 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 21:14 [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Douglas Anderson
2020-04-21 21:14 ` [PATCH v2 1/9] kgdb: Disable WARN_CONSOLE_UNLOCKED for all kgdb Douglas Anderson
2020-04-27 13:40   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 2/9] Revert "kgdboc: disable the console lock when in kgdb" Douglas Anderson
2020-04-27 13:41   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 3/9] kgdboc: Use a platform device to handle tty drivers showing up late Douglas Anderson
2020-04-27 14:19   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 4/9] kgdb: Delay "kgdbwait" to dbg_late_init() by default Douglas Anderson
2020-04-27 15:42   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 5/9] arm64: Add call_break_hook() to early_brk64() for early kgdb Douglas Anderson
2020-04-27 16:52   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 6/9] kgdboc: Add earlycon_kgdboc to support early kgdb using boot consoles Douglas Anderson
2020-04-27 16:36   ` Daniel Thompson
2020-04-28 21:32     ` Doug Anderson
2020-04-21 21:14 ` Douglas Anderson [this message]
2020-04-27 16:46   ` [PATCH v2 7/9] Documentation: kgdboc: Document new earlycon_kgdboc parameter Daniel Thompson
2020-04-28 21:32     ` Doug Anderson
2020-04-21 21:14 ` [PATCH v2 8/9] serial: qcom_geni_serial: Support earlycon_kgdboc Douglas Anderson
2020-04-27 16:48   ` Daniel Thompson
2020-04-21 21:14 ` [PATCH v2 9/9] serial: 8250_early: " Douglas Anderson
2020-04-27 16:50   ` Daniel Thompson
2020-04-23 13:50 ` [PATCH v2 0/9] kgdb: Support late serial drivers; enable early debug w/ boot consoles Greg KH
2020-04-24  8:32 ` Sumit Garg
2020-04-24 10:13   ` Daniel Thompson

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