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During Display Port link training the handling of HPD pulses should be
prevented, as that handling can interfere with the link training:
- Accessing DPCD registers outside the range of link training registers
are not allowed by the Standard (see DP Standard v2.1, 3.5.2.16.1,
3.6.6.1). The pulse handler reads the DPRX capability registers, which
are outside of the allowed range.
- Switching of the LTTPR transparent/non-transparent mode may reset the
LTTPRs on the link, thus aborting any ongoing link training. The pulse
handler does set the LTTPR mode, thus it could unexpectedly abort the
ongoing link training.
Block/unblock the HPD pulse handling for the duration of the link
training to prevent the above DPCD register accesses / LTTPR mode
change.
Apart from the above scenarios, there are other ways a non-link training
DPCD register could be accessed during link training: via the DRM AUX
device node, or via DPCD register probing (as performed by
drm_dp_dpcd_probe()). These will be addressed by a follow-up change.
v2: Rebase on the intel_hpd_suspend/resume -> intel_hpd_block/unblock()
rename change.
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250304152917.3407080-5-imre.deak@intel.com
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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.