[Bug 107585] Wrong max TMDS clock rate on ThinkPad W541 mini-DisplayPort output

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107585

--- Comment #4 from Simon <Simon80 at gmail.com> ---
Yeah, maybe in general the user can plug in random adaptors, but in this case
the adaptor is internal, part of the laptop's mini-DisplayPort.

Sure, a black screen is suboptimal, but if someone is trying to use an old
adapter to drive a 4K screen, they're going to need to replace the adaptor
regardless of whether the result is a black screen or 1080p output. If they get
a black screen, they can work around it by switching to a lower output mode, as
long as the 4K output isn't the only display attached to the system. So for any
laptop user the black screen isn't so severe, because the user can use the
internal screen to pick a different mode. I'd guess that desktop users
generally would have an HDMI port they can use instead of a passive connection
via DisplayPort.

Meanwhile, in the case of TMDS underclocking, there's no direct clue that
something is wrong, and almost no workaround. There were no clues in the kernel
log without debugging enabled, and I couldn't figure out a workaround without
running a working kernel and copying the modelinr out. For many people, the
workaround would be to go back to Windows or OS X and just conclude that Linux
has inferior hardware support. Is there any way we can figure out how the
Windows driver is managing to do the right thing in this case?

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