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Lyude Paul f88c31b43b drm/nouveau: Don't retry infinitely when receiving no data on i2c over AUX commit `c358ebf596` upstream. While I had thought I had fixed this issue in: commit `342406e4fb` ("drm/nouveau/i2c: Disable i2c bus access after ->fini()") It turns out that while I did fix the error messages I was seeing on my P50 when trying to access i2c busses with the GPU in runtime suspend, I accidentally had missed one important detail that was mentioned on the bug report this commit was supposed to fix: that the CPU would only lock up when trying to access i2c busses _on connected devices_ _while the GPU is not in runtime suspend_. Whoops. That definitely explains why I was not able to get my machine to hang with i2c bus interactions until now, as plugging my P50 into it's dock with an HDMI monitor connected allowed me to finally reproduce this locally. Now that I have managed to reproduce this issue properly, it looks like the problem is much simpler then it looks. It turns out that some connected devices, such as MST laptop docks, will actually ACK i2c reads even if no data was actually read: [ 275.063043] nouveau 0000:01:00.0: i2c: aux 000a: 1: 0000004c 1 [ 275.063447] nouveau 0000:01:00.0: i2c: aux 000a: 00 01101000 10040000 [ 275.063759] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000001 [ 275.064024] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000 [ 275.064285] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000 [ 275.064594] nouveau 0000:01:00.0: i2c: aux 000a: rd 00000000 Because we don't handle the situation of i2c ack without any data, we end up entering an infinite loop in nvkm_i2c_aux_i2c_xfer() since the value of cnt always remains at 0. This finally properly explains how this could result in a CPU hang like the ones observed in the aforementioned commit. So, fix this by retrying transactions if no data is written or received, and give up and fail the transaction if we continue to not write or receive any data after 32 retries. Signed-off-by: Lyude Paul <lyude@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Ben Skeggs <bskeggs@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2019-08-29 08:28:51 +02:00
arch	KVM: arm: Don't write junk to CP15 registers on reset	2019-08-29 08:28:48 +02:00
block	block, bfq: handle NULL return value by bfq_init_rq()	2019-08-29 08:28:46 +02:00
certs	export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR()	2018-08-22 23:21:44 +09:00
crypto	crypto: chacha20poly1305 - fix atomic sleep when using async algorithm	2019-07-26 09:14:19 +02:00
Documentation	Documentation: Add swapgs description to the Spectre v1 documentation	2019-08-06 19:06:58 +02:00
drivers	drm/nouveau: Don't retry infinitely when receiving no data on i2c over AUX	2019-08-29 08:28:51 +02:00
firmware	kbuild: remove all dummy assignments to obj-	2017-11-18 11:46:06 +09:00
fs	ceph: don't try fill file_lock on unsuccessful GETFILELOCK reply	2019-08-29 08:28:50 +02:00
include	drm/i915/cfl: Add a new CFL PCI ID.	2019-08-25 10:48:01 +02:00
init	initramfs: free initrd memory if opening /initrd.image fails	2019-06-15 11:54:01 +02:00
ipc	ipc/mqueue.c: only perform resource calculation if user valid	2019-08-06 19:06:52 +02:00
kernel	cpufreq: schedutil: Don't skip freq update when limits change	2019-08-25 10:47:46 +02:00
lib	test_firmware: fix a memory leak bug	2019-08-16 10:12:49 +02:00
LICENSES	LICENSES: Remove CC-BY-SA-4.0 license text	2018-10-18 11:28:50 +02:00
mm	Revert "kmemleak: allow to coexist with fault injection"	2019-08-25 10:47:58 +02:00
net	libceph: fix PG split vs OSD (re)connect race	2019-08-29 08:28:50 +02:00
samples	samples, bpf: suppress compiler warning	2019-07-14 08:11:04 +02:00
scripts	kbuild: Check for unknown options with cc-option usage in Kconfig and clang	2019-08-25 10:47:56 +02:00
security	selinux: fix memory leak in policydb_init()	2019-08-06 19:06:54 +02:00
sound	ASoC: ti: davinci-mcasp: Correct slot_width posed constraint	2019-08-29 08:28:32 +02:00
tools	selftests: kvm: Adding config fragments	2019-08-29 08:28:48 +02:00
usr	initramfs: move gen_initramfs_list.sh from scripts/ to usr/	2018-08-22 23:21:44 +09:00
virt	KVM: arm/arm64: Sync ICH_VMCR_EL2 back when about to block	2019-08-25 10:47:59 +02:00
.clang-format	clang-format: Set IndentWrappedFunctionNames false	2018-08-01 18:38:51 +02:00
.cocciconfig	scripts: add Linux .cocciconfig for coccinelle	2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes	.gitattributes: set git diff driver for C source code files	2016-10-07 18:46:30 -07:00
.gitignore	Kbuild updates for v4.17 (2nd)	2018-04-15 17:21:30 -07:00
.mailmap	libnvdimm-for-4.19_misc	2018-08-25 18:13:10 -07:00
COPYING	COPYING: use the new text with points to the license files	2018-03-23 12:41:45 -06:00
CREDITS	9p: remove Ron Minnich from MAINTAINERS	2018-08-17 16:20:26 -07:00
Kbuild	Kbuild updates for v4.15	2017-11-17 17:45:29 -08:00
Kconfig	kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt	2018-08-02 08:06:55 +09:00
MAINTAINERS	platform/x86: Add Intel AtomISP2 dummy / power-management driver	2019-04-20 09:16:02 +02:00
Makefile	Linux 4.19.68	2019-08-25 10:48:06 +02:00
README	Docs: Added a pointer to the formatted docs to README	2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.