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Tomi Valkeinen 7423c2883c drm/omap: fix memory barrier bug in DMM driver 
[ Upstream commit 538f66ba20 ]

A DMM timeout "timed out waiting for done" has been observed on DRA7
devices. The timeout happens rarely, and only when the system is under
heavy load.

Debugging showed that the timeout can be made to happen much more
frequently by optimizing the DMM driver, so that there's almost no code
between writing the last DMM descriptors to RAM, and writing to DMM
register which starts the DMM transaction.

The current theory is that a wmb() does not properly ensure that the
data written to RAM is observable by all the components in the system.

This DMM timeout has caused interesting (and rare) bugs as the error
handling was not functioning properly (the error handling has been fixed
in previous commits):

 * If a DMM timeout happened when a GEM buffer was being pinned for
   display on the screen, a timeout error would be shown, but the driver
   would continue programming DSS HW with broken buffer, leading to
   SYNCLOST floods and possible crashes.

 * If a DMM timeout happened when other user (say, video decoder) was
   pinning a GEM buffer, a timeout would be shown but if the user
   handled the error properly, no other issues followed.

 * If a DMM timeout happened when a GEM buffer was being released, the
   driver does not even notice the error, leading to crashes or hang
   later.

This patch adds wmb() and readl() calls after the last bit is written to
RAM, which should ensure that the execution proceeds only after the data
is actually in RAM, and thus observable by DMM.

The read-back should not be needed. Further study is required to understand
if DMM is somehow special case and read-back is ok, or if DRA7's memory
barriers do not work correctly.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2018-11-21 09:19:10 +01:00
arch powerpc/mm: Don't report hugepage tables as memory leaks when using kmemleak 2018-11-21 09:19:09 +01:00
block block, bfq: correctly charge and reset entity service in all cases 2018-11-13 11:08:28 -08:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: speck - remove Speck 2018-11-13 11:08:46 -08:00
Documentation media: replace ADOBERGB by OPRGB 2018-11-13 11:08:54 -08:00
drivers drm/omap: fix memory barrier bug in DMM driver 2018-11-21 09:19:10 +01:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: fix use-after-free when dumping free space 2018-11-13 11:09:00 -08:00
include media: hdmi.h: rename ADOBE_RGB to OPRGB and ADOBE_YCC to OPYCC 2018-11-13 11:08:54 -08:00
init Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel tracing/kprobes: Check the probe on unloaded module correctly 2018-11-21 09:19:09 +01:00
lib locking/lockdep: Fix debug_locks off performance problem 2018-11-13 11:08:20 -08:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/hmm: fix race between hmm_mirror_unregister() and mmu_notifier callback 2018-11-13 11:08:47 -08:00
net net: sched: Remove TCA_OPTIONS from policy 2018-11-13 11:09:00 -08:00
samples samples: disable CONFIG_SAMPLES for UML 2018-10-11 02:15:46 +09:00
scripts Kbuild fixes for v4.19 (2nd) 2018-10-11 19:23:07 +02:00
security ima: open a new file instance if no read permissions 2018-11-13 11:08:46 -08:00
sound ASoC: sta32x: set ->component pointer in private struct 2018-11-13 11:08:42 -08:00
tools selftests/powerpc: Fix ptrace tm failure 2018-11-13 11:08:55 -08:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: arm64: Fix caching of host MDCR_EL2 value 2018-11-13 11:08:47 -08:00
.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 Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.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 MAINTAINERS: Add an entry for the code of conduct 2018-10-22 07:33:36 +01:00
Makefile Linux 4.19.2 2018-11-13 11:09:00 -08:00
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.