From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Sanford Rockowitz <rockowitz@minsoft.com>
Cc: Intel-gfx@lists.freedesktop.org
Subject: Re: i915 I2C failures with recent chips and docking stations
Date: Fri, 5 May 2017 23:27:56 +0300 [thread overview]
Message-ID: <20170505202756.GM12629@intel.com> (raw)
In-Reply-To: <590C2F83.3090103@minsoft.com>
On Fri, May 05, 2017 at 03:53:39AM -0400, Sanford Rockowitz wrote:
> I am the author of ddcutil (www.ddcutil.com), a Linux utility that
> manages monitor settings using DDC/CI. I am seeing a pattern of user
> error reports in which I2C communication is not working when a system
> with a recent Intel chip, using the i915 driver, is plugged into a
> docking station. Communication works when the video cable is plugged
> directly into the laptop. There also seems to be a correlation with
> whether a DisplayPort cable is being used (i.e. the I2C-over-aux path is
> being executed), though this correlation is not as clear.
Apart from the MST issues already mentioned, I have noticed (at least
with some displays) that the DDC/CI slaves don't seem to do clock
stretching properly, and that the default 100kHz clock tends to be
too much for them. A while ago I tried to cook up some hacks to work
around these issues both in our i2c and i2c-over-aux code. The idea
was to just reduce the bus speed whenever DDC/CI is being attempted.
My hacks are here:
git://github.com/vsyrjala/linux.git i2c_bus_speed
But do note that I've not seem many DP dongles that actually support
the i2c bus speed control, so the usefulness of the i2c-over-aux
part of that code might be a little questionable. I also didn't
implement anything for the MST case, so those would still be using
whatever is the default bus speed.
--
Ville Syrjälä
Intel OTC
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prev parent reply other threads:[~2017-05-05 20:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-05 7:53 i915 I2C failures with recent chips and docking stations Sanford Rockowitz
2017-05-05 9:59 ` Jani Nikula
2017-05-05 14:05 ` Sanford Rockowitz
2017-05-05 16:49 ` Jani Nikula
2017-05-05 19:47 ` Sanford Rockowitz
2017-05-05 20:09 ` Jani Nikula
2017-05-05 20:27 ` Ville Syrjälä [this message]
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