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Imre Deak d34d6feaf4
drm/dp: Change AUX DPCD probe address from LANE0_1_STATUS to TRAINING_PATTERN_SET 
Commit a3ef3c2da6 ("drm/dp: Change AUX DPCD probe address from
DPCD_REV to LANE0_1_STATUS") stopped using the DPCD_REV register for
DPCD probing, since this results in link training failures at least when
using an Intel Barlow Ridge TBT hub at UHBR link rates (the
DP_INTRA_HOP_AUX_REPLY_INDICATION never getting cleared after the failed
link training). Since accessing DPCD_REV during link training is
prohibited by the DP Standard, LANE0_1_STATUS (0x202) was used instead,
as it falls within the Standard's valid register address range
(0x102-0x106, 0x202-0x207, 0x200c-0x200f, 0x2216) and it fixed the link
training on the above TBT hub.

However, reading the LANE0_1_STATUS register also has a side-effect at
least on a Novatek eDP panel, as reported on the Closes: link below,
resulting in screen flickering on that panel. One clear side-effect when
doing the 1-byte probe reads from LANE0_1_STATUS during link training
before reading out the full 6 byte link status starting at the same
address is that the panel will report the link training as completed
with voltage swing 0. This is different from the normal, flicker-free
scenario when no DPCD probing is done, the panel reporting the link
training complete with voltage swing 2.

Using the TRAINING_PATTERN_SET register for DPCD probing doesn't have
the above side-effect, the panel will link train with voltage swing 2 as
expected and it will stay flicker-free. This register is also in the
above valid register range and is unlikely to have a side-effect as that
of LANE0_1_STATUS: Reading LANE0_1_STATUS is part of the link training
CR/EQ sequences and so it may cause a state change in the sink - even if
inadvertently as I suspect in the case of the above Novatek panel. As
opposed to this, reading TRAINING_PATTERN_SET is not part of the link
training sequence (it must be only written once at the beginning of the
CR/EQ sequences), so it's unlikely to cause any state change in the
sink.

As a side-note, this Novatek panel also lacks support for TPS3, while
claiming support for HBR2, which violates the DP Standard (the Standard
mandating TPS3 for HBR2).

Besides the Novatek panel (PSR 1), which this change fixes, I also
verified the change on a Samsung (PSR 1) and an Analogix (PSR 2) eDP
panel as well as on the Intel Barlow Ridge TBT hub.

Note that in the drm-tip tree (targeting the v6.17 kernel version) the
i915 and xe drivers keep DPCD probing enabled only for the panel known
to require this (HP ZR24w), hence those drivers in drm-tip are not
affected by the above problem.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Fixes: a3ef3c2da6 ("drm/dp: Change AUX DPCD probe address from DPCD_REV to LANE0_1_STATUS")
Reported-and-tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14558
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250708212331.112898-1-imre.deak@intel.com
(cherry picked from commit bba9aa4165)
[Imre: Rebased on drm-intel-fixes]
Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo: Changed original commit hash to match with the one propagated in fixes]
2025-07-15 09:37:57 -04:00
arch - Update Kirill's email address 2025-07-13 10:41:19 -07:00
block block-6.16-20250626 2025-06-27 09:02:33 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: wp512 - Use API partial block handling 2025-06-23 16:56:56 +08:00
Documentation Fixes for a few clk drivers and bindings: 2025-07-13 11:37:35 -07:00
drivers drm/dp: Change AUX DPCD probe address from LANE0_1_STATUS to TRAINING_PATTERN_SET 2025-07-15 09:37:57 -04:00
fs 19 hotfixes. A whopping 16 are cc:stable and the remainder address 2025-07-12 10:30:47 -07:00
include - Fix a case of recursive locking in the MSI code 2025-07-13 10:36:55 -07:00
init futex: Temporary disable FUTEX_PRIVATE_HASH 2025-07-01 15:02:05 +02:00
io_uring io_uring-6.16-20250710 2025-07-11 10:29:30 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel - Prevent perf_sigtrap() from observing an exiting task and warning 2025-07-13 10:34:47 -07:00
lib maple_tree: fix mt_destroy_walk() on root leaf node 2025-07-09 21:07:52 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
mm Revert "sched/numa: add statistics of numa balance task" 2025-07-09 21:07:56 -07:00
net netlink: make sure we allow at least one dump skb 2025-07-11 07:31:47 -07:00
rust Merge tag 'drm-misc-fixes-2025-07-10' of https://gitlab.freedesktop.org/drm/misc/kernel into drm-fixes 2025-07-11 14:11:19 +02:00
samples samples/damon: fix damon sample mtier for start failure 2025-07-09 21:07:55 -07:00
scripts scripts: gdb: vfs: support external dentry names 2025-07-09 21:07:54 -07:00
security selinux: change security_compute_sid to return the ssid or tsid on match 2025-06-19 16:13:16 -04:00
sound ALSA: hda/realtek: Enable headset Mic on Positivo K116J 2025-07-07 14:09:09 +02:00
tools - Update Kirill's email address 2025-07-13 10:41:19 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-06-24 12:20:17 -07:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap MAINTAINERS: Update Kirill Shutemov's email address for TDX 2025-07-11 07:25:51 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.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 CREDITS: Add entry for Shannon Nelson 2025-06-21 07:34:28 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS - Update Kirill's email address 2025-07-13 10:41:19 -07:00
Makefile Linux 6.16-rc6 2025-07-13 14:25:58 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -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 reStructuredText 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.