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Lyude Paul c358ebf596 drm/nouveau: Don't retry infinitely when receiving no data on i2c over AUX 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>		2019-08-23 12:42:43 +10:00
arch	Merge branch 'topic/remove-fbcon-notifiers' into drm-misc-next	2019-06-19 12:33:05 +02:00
block	blk-mq: remove WARN_ON(!q->elevator) from blk_mq_sched_free_requests	2019-06-13 03:05:58 -06:00
certs
crypto	SPDX update for 5.2-rc4	2019-06-08 12:52:42 -07:00
Documentation	Merge tag 'drm-msm-next-2019-06-25' of https://gitlab.freedesktop.org/drm/msm into drm-next	2019-06-28 10:16:40 +10:00
drivers	drm/nouveau: Don't retry infinitely when receiving no data on i2c over AUX	2019-08-23 12:42:43 +10:00
fs	Fix rounding error in gfs2_iomap_page_prepare	2019-06-14 17:27:12 -10:00
include	Revert "Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next"	2019-07-16 04:07:13 +10:00
init	Char/Misc driver fixes for 5.2-rc4	2019-06-08 12:50:36 -07:00
ipc	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441	2019-06-05 17:37:17 +02:00
kernel	Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2019-06-16 07:22:56 -10:00
lib	lib/genalloc: introduce chunk owners	2019-06-13 17:34:56 -10:00
LICENSES
mm	Revert "Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next"	2019-07-16 04:07:13 +10:00
net	SPDX update for 5.2-rc4	2019-06-08 12:52:42 -07:00
samples	SPDX update for 5.2-rc4	2019-06-08 12:52:42 -07:00
scripts	scripts/decode_stacktrace.sh: prefix addr2line with $CROSS_COMPILE	2019-06-13 17:34:56 -10:00
security	Smack: Restore the smackfsdef mount option and add missing prefixes	2019-06-14 14:25:04 -10:00
sound	sound fixes for 5.2-rc5	2019-06-14 05:37:06 -10:00
tools	mm/devm_memremap_pages: fix final page put race	2019-06-13 17:34:56 -10:00
usr
virt	treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 333	2019-06-05 17:37:06 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
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COPYING
CREDITS	MAINTAINERS: Farewell Martin Schwidefsky	2019-05-31 10:14:11 +02:00
Kbuild
Kconfig
MAINTAINERS	Revert "Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next"	2019-07-16 04:07:13 +10:00
Makefile	Linux 5.2-rc5	2019-06-16 08:49:45 -10:00
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