need guidance re amdgpu i2c

Tue Sep 13 20:43:31 UTC 2016

aelaric,

I will join the IRC channel. 

As to uses that you see for ddctool, the short answer is that it's not
going to be of help (except possibly for underscan).

Now for the long answer.

To address your thought that ddctool might be able to help with monitor
switching and resolution, a bit of background will simplify my
answers.   Forgive me if this is all known.  Monitors provide a set of
controls, referred to as Virtual Control Panel (VCP) Features.  These
are defined in VESA's Monitor Control and Command Set (MCCS)
specification.   Typically, these are communicated between monitor and
host using the DDC/CI protocol on address x37 of the I2C bus. 
(Alternatively, the commands may be communicated over USB, but that is
not relevant here.)  Monitors typically implement only a small subset of
defined controls.   There is a range of numbers reserved for
manufacturer specific controls.  ddctool can read and set these, but
doesn't know how to interpret them.

Laptops do not use the I2C bus to communicate VCP features.   The EDID
is typically communicated on address x50 of the I2C bus, but I've yet to
see a laptop where address x37 for DDC/CI is implemented.   So ddctool
can read the laptop monitor's EDID, but that's it.

VCP Feature Code x60 allows for changing the input source on a monitor,
e.g. DVI-1, DVI-2.  But that will not address what you want to do, which
is to change where the laptop directs its output. 

As for controlling underscan on an external monitor, there's some hope. 
VCP Feature Code xDA (Scan mode) allows for setting Normal Operation,
Underscan, Overscan, or Widescreen.  I believe this is what you are
looking for.  However, this control is not widely implemented.   Of 4
monitors I just checked, none provide this feature.   Generally
specking, if something can be queried or set using the On Screen Display
(OCD) there will also be ability to read and set this value using a VCP
feature, but it may be implemented using a manufacturer specific code. 

Regards,
Sanford

On 09/13/2016 10:50 AM, aelaric wrote:
> Sanford,
>
> We have started an IRC channel for the support of amdgpu/amdgpu-pro.
> (Freenode, #amdgpu) We are currently in dire need of a way to switch
> to HDMI monitor and deactivate LDS screen on laptops while using
> amdgpu. We could really use you in the channel, to provide you with
> testing results, and also I am hoping you can help us resolve our
> monitor switching/resolution problems.
>
> We would be more than glad to run ddctool on our hdmi setups as root
> and provide you with the results.
>
> Also, can ddctool affect overscan/underscan settings on an hdmi monitor?
>
> Kind Regards,
>
> --aelaric
>
> On 09/13/2016 06:47 AM, Sanford Rockowitz wrote:
>> First, apologies in advance if this is not the most appropriate list for
>> my questions.  Redirection appreciated.
>>
>> I am the author of ddctool <www.ddctool.com>, a utility to manipulate
>> monitor settings using DDC/CI over I2C.
>>
>> My understanding is that amdgpu provides /dev/i2c-* devices in the usual
>> way, so that ddctool should just work without changes.  But of course
>> this needs to be tested.
>>
>> In this regard I have a number of questions and a request.
>>
>> Does the i2c interface depend in some way on whether one is running the
>> AMDGPU-PRO driver?
>>
>> The most current AMD card that I own in a R9 280, which is a first
>> generation GCN device.   Phoronix suggests that first generation GCN
>> support is in the works.  Will this be soon?   If not, would the current
>> development code for amdgpu be sufficient for me to test the i2c
>> support?   If so, what would I have to do to build and install it?
>>
>> Or should I just plunk down a few dollars for a relatively inexpensive
>> R7 260, which I understand is supported by the current amdgpu?
>>
>> Alternatively, if someone running the amdgpu driver would be willing to
>> install and test ddctool on their system I'd be most appreciative.  The
>> git repository is here: https://github.com/rockowitz/ddctool, and
>> there's extensive documentation on the website, www.ddctool.com.
>>
>> A couple of command line options of note:
>>
>>   "--stats" reports extensive performance statistics, including counts
>> of i2c retries required
>>   "--ddc"  reports DDC protocol data errors
>>
>> If ddctool installs but does not seem to be working, command "ddctool
>> environment" may provide some clues.
>>
>> Finally, the "ddctool interrogate" command fully exercises ddctool and
>> probes the i2c environment.  Depending on permissions, running it as
>> root may provide additional detail.  If you can capture the output and
>> send it to me that would be most helpful.
>>
>> Thanks in advance,
>> Sanford Rockowitz
>>
>>
>>
>> _______________________________________________
>> amd-gfx mailing list
>> amd-gfx at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
>>
>
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