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471bdd0df0
Some TypeC -> native DP adapters, at least the Club 3D CAC-1557 adapter, incorrectly filter out HPD short pulses with a duration less than ~540 usec, leading to MST probe failures. According to the DP Standard 2.0 section 5.1.4: - DP sinks should generate short pulses in the 500 usec -> 1 msec range - DP sources should detect short pulses in the 250 usec -> 2 msec range According to the DP Alt Mode on TypeC Standard section 3.9.2, adapters should detect and forward short pulses according to how sources should detect them as specified in the DP Standard (250 usec -> 2 msec). Based on the above filtering out short pulses with a duration less than 540 usec is incorrect. To make such adapters work add support for a driver polling on MST inerrupt flags, and wire this up in the i915 driver. The sink can clear an interrupt it raised after 110 msec if the source doesn't respond, so use a 50 msec poll period to avoid missing an interrupt. Polling of the MST interrupt flags is explicitly allowed by the DP Standard. This fixes MST probe failures I saw using this adapter and a DELL U2515H monitor. v2: - Fix the wait event timeout for the no-poll case. v3 (Ville): - Fix the short pulse duration limits in the commit log prescribed by the DP Standard. - Add code comment explaining why/how polling is used. - Factor out a helper to schedule the port's hpd irq handler and move it to the rest of hotplug handlers. - Document the new MST callback. - s/update_hpd_irq_state/poll_hpd_irq/ Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Imre Deak <imre.deak@intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Lyude Paul <lyude@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200604184500.23730-2-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 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.