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Douglas Anderson 7b3423eff2 kgdboc: Use a platform device to handle tty drivers showing up late 
[ Upstream commit 68e55f61c1 ]

If you build CONFIG_KGDB_SERIAL_CONSOLE into the kernel then you
should be able to have KGDB init itself at bootup by specifying the
"kgdboc=..." kernel command line parameter.  This has worked OK for me
for many years, but on a new device I switched to it stopped working.

The problem is that on this new device the serial driver gets its
probe deferred.  Now when kgdb initializes it can't find the tty
driver and when it gives up it never tries again.

We could try to find ways to move up the initialization of the serial
driver and such a thing might be worthwhile, but it's nice to be
robust against serial drivers that load late.  We could move kgdb to
init itself later but that penalizes our ability to debug early boot
code on systems where the driver inits early.  We could roll our own
system of detecting when new tty drivers get loaded and then use that
to figure out when kgdb can init, but that's ugly.

Instead, let's jump on the -EPROBE_DEFER bandwagon.  We'll create a
singleton instance of a "kgdboc" platform device.  If we can't find
our tty device when the singleton "kgdboc" probes we'll return
-EPROBE_DEFER which means that the system will call us back later to
try again when the tty device might be there.

We won't fully transition all of the kgdboc to a platform device
because early kgdb initialization (via the "ekgdboc" kernel command
line parameter) still runs before the platform device has been
created.  The kgdb platform device is merely used as a convenient way
to hook into the system's normal probe deferral mechanisms.

As part of this, we'll ever-so-slightly change how the "kgdboc=..."
kernel command line parameter works.  Previously if you booted up and
kgdb couldn't find the tty driver then later reading
'/sys/module/kgdboc/parameters/kgdboc' would return a blank string.
Now kgdb will keep track of the string that came as part of the
command line and give it back to you.  It's expected that this should
be an OK change.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200507130644.v4.3.I4a493cfb0f9f740ce8fd2ab58e62dc92d18fed30@changeid
[daniel.thompson@linaro.org: Make config_mutex static]
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2020-06-22 09:31:06 +02:00
Documentation dt-bindings: display: mediatek: control dpi pins mode to avoid leakage 2020-06-22 09:30:58 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch mips: cm: Fix an invalid error code of INTVN_*_ERR 2020-06-22 09:31:03 +02:00
block iocost: don't let vrate run wild while there's no saturation signal 2020-06-22 09:31:06 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: drbg - fix error return code in drbg_alloc_state() 2020-06-17 16:40:31 +02:00
drivers kgdboc: Use a platform device to handle tty drivers showing up late 2020-06-22 09:31:06 +02:00
fs xfs: fix duplicate verification from xfs_qm_dqflush() 2020-06-22 09:31:03 +02:00
include kgdb: Fix spurious true from in_dbg_master() 2020-06-22 09:31:03 +02:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel sched/core: Fix illegal RCU from offline CPUs 2020-06-22 09:31:01 +02:00
lib lib/mpi: Fix 64-bit MIPS build with Clang 2020-06-22 09:31:00 +02:00
mm mm/slub: fix a memory leak in sysfs_slab_add() 2020-06-17 16:40:36 +02:00
net netfilter: nft_nat: return EOPNOTSUPP if type or flags are not supported 2020-06-22 09:31:00 +02:00
samples samples: bpf: Fix build error 2020-06-03 08:21:15 +02:00
scripts bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
security selinux: fix error return code in policydb_read() 2020-06-22 09:31:01 +02:00
sound ALSA: usb-audio: Add vendor, product and profile name for HP Thunderbolt Dock 2020-06-17 16:40:28 +02:00
tools iocost_monitor: drop string wrap around numbers when outputting json 2020-06-22 09:31:01 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm64: Save the host's PtrAuth keys in non-preemptible context 2020-06-17 16:40:38 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.47 2020-06-17 16:40:38 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.