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Linux mainline fork with MSM8998 patches | https://mainline.space | Currently supported devices: OnePlus 5/5T, Xiaomi Mi 6, F(x)tec Pro¹ (2019 QX1000 model) & Sony Xperia XZ Premium (UNTESTED!)
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Douglas Anderson cb8e30ddb7 drm/bridge: ps8640: Add back the 50 ms mystery delay after HPD 
Back in commit 826cff3f7e ("drm/bridge: parade-ps8640: Enable
runtime power management") we removed a mysterious 50 ms delay because
"Parade's support [couldn't] explain what the delay [was] for".

While I'm always a fan of removing mysterious delays, I suspect that
we need this mysterious delay to avoid some problems.

Specifically, what I found recently is that on sc7180-trogdor-homestar
sometimes the AUX backlight wasn't initializing properly. Some
debugging showed that the drm_dp_dpcd_read() function that the AUX
backlight driver was calling was returning bogus data about 1% of the
time when I booted up. This confused
drm_panel_dp_aux_backlight(). From continued debugging:
- If I retried the read then the read worked just fine.
- If I added a loop to perform the same read that
  drm_panel_dp_aux_backlight() was doing 30 times at bootup I could
  see that some percentage of the time the first read would give bogus
  data but all 29 additional reads would always be fine.
- If I added a large delay _after_ powering on the panel but before
  powering on PS8640 I could still reproduce the problem.
- If I added a delay after PS8640 powered on then I couldn't reproduce
  the problem.
- I couldn't reproduce the problem on a board with the same panel but
  the ti-sn65dsi86 bridge chip.

To me, the above indicated that there was a problem with PS8640 and
not the panel.

I don't really have any insight into what's going on in the MCU, but
my best guess is that when the MCU itself sees the HPD go high that it
does some AUX transfers itself and this is confusing things.

Let's go back and add back in the mysterious 50 ms delay. We only want
to do this the first time we see HPD go high after booting the MCU,
not every time we double-check HPD.

With this, the backlight initializes reliably on homestar.

Fixes: 826cff3f7e ("drm/bridge: parade-ps8640: Enable runtime power management")
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221017121813.1.I59700c745fbc31559a5d5c8e2a960279c751dbd5@changeid
2022-10-21 08:07:12 -07:00
arch Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
block Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto treewide: use get_random_bytes() when possible 2022-10-11 17:42:58 -06:00
Documentation Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
drivers drm/bridge: ps8640: Add back the 50 ms mystery delay after HPD 2022-10-21 08:07:12 -07:00
fs Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
include drm/panfrost: replace endian-specific types with native ones 2022-10-20 11:02:11 +01:00
init - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
io_uring io_uring/rw: ensure kiocb_end_write() is always called 2022-10-12 16:30:56 -06:00
ipc - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
kernel Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
lib Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
net Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
rust Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
samples VFIO updates for v6.1-rc1 2022-10-12 14:46:48 -07:00
scripts Kbuild fixes for v6.1 2022-10-16 11:12:22 -07:00
security - Yu Zhao's Multi-Gen LRU patches are here. They've been under test in 2022-10-10 17:53:04 -07:00
sound sound fixes for 6.1-rc1 2022-10-14 13:22:14 -07:00
tools perf tools changes for v6.1: 2nd batch 2022-10-16 15:14:29 -07:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt VFIO updates for v6.1-rc1 2022-10-12 14:46:48 -07:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS OpenRISC 6.1 Updates 2022-10-15 16:47:33 -07:00
Makefile Linux 6.1-rc1 2022-10-16 15:36:24 -07:00
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.