[Bug 172421] radeon: allow to set the TMDS frequency by a special kernel parameter

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=172421

John (sirfixabyte at gmail.com) changed:

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                 CC|                            |sirfixabyte at gmail.com

--- Comment #19 from John (sirfixabyte at gmail.com) ---
I read all the previous comments - for and against the adoption of the patch. 
Question: Why is it easy to find a pixel clock patch for WINDOWS
(www.monitortests.com AMD/ATI Pixel Clock Patcher by someone named 'ToastyX')
-available and supported since 2012 - and successfully running 4K screens
(since January 2016) on the same Radeon cards being discussed here ? Many
people on that webpage discussing it. Seems to work. I personally tested on a
few older Radeon cards and it works at 3840x2160 for me.  I have NOT yet run it
for hours (I rarely run Windows, and then only to test of fix PC's for others).
I have not connected temperature sensors to heat sinks yet.

If the pixel clock generator circuitry is on the same die as everything else,
then it shares a heat sink.  The whole thing designed such that with
recommended airflow across that heat sink, the GPU remains functional. BUT,
that can mean running 3 separate displays - utilizing the full capacity of the
GPU. 

IF this patch from Elmar Stellnberger were to be used to run a SINGLE 4K LCD at
3840 x 2160 at 30% overclock on the pixel clock generator, maybe the overall
GPU would be generating much less than maximum heat, and the heatsink/fan could
easily keep it cool.

Does anyone have a maximum pixel clock specification for the various pixel
clock generator designs on the various ATI/AMD dies ? 
Did ATI set limits due to HDMI cables and overall ability of heatsink to
dissipate the heat when running the GPU at max speed / load on 3 screens ?
Is there a listed maximum voltage that the PLL can run at - long term - without
damage ? for most integrated circuits data sheets I have ever read, there is a
relationship between max speed and temperature of the die.

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