Created attachment 142540 [details]
Dmesg from boot
This report id follow up to discussion on reported (and fixed) bug https://bugs.freedesktop.org/show_bug.cgi?id=107476
I'm actually running into the very same problem, but with already patched kernel 4.18.16-200. I look into this several hours and seems to be similar problem.
With resolution 1920x1080 color range is trimmed, but with lover resolution (e.g. 1600x900), colors seems to be pretty fine.
I'm attaching requested dmesg log with drm.debug=0x1e parameter.
It's only problem with Display port, HDMI is working well.
I have also discrete ATI card, but this one is not attached to display port (UEFI is preventing to use switcheroo), so always Intel card is in use.
Please let me know if you need any further data.
What kind of adapter are you using for DP->HDMI?
It's DP to HDMI male-male cable, nothing special: https://www.tsbohemia.cz/kabel-c-tech-displayport-na-hdmi-m-m-1m_d198856.html
There isn't any further specification.
I'm using HP docking station (http://www8.hp.com/us/en/products/oas/product-detail.html?oid=5422417) and then just connecting DP using this cable.
So you have a DP MST branch device in the dock and an active DP->HDMI protocol converter cable, and you call that "nothing special"? :)
My guess is that the CEA range main stream attribute is lost in the protocol translation.
OK, I'm trying to understand what you just wrote. Does it simply mean, that my cable is too "weak" to be used with by DP output from docking station, please ?
Actually I'm an "simple" user, trying to understand why my laptop to external monitor is not working properly.
Can I somehow switch something in system, to get correct protocol translation? Or do I need to buy some new cable with some specific specification?
As I wrote, changing to lower resolution brings back normal color range.
At some point during the DP->HDMI conversion one crucial bit gets lost. It's not about the signal being weak, it's about the conversion losing information. It would be useful to try the cable without the dock if possible. It could be the dock, or the cable, or the combination of the two that breaks this.
The resolution affects this because the relevant specs say the source needs to use CEA (or broadcast or limited) range RGB for certain video modes, and full range otherwise. On the mode that works for you, we're sending full range. On the mode that doesn't work, we're sending CEA range plus the bit to indicate to the display it's CEA range.
Thank you for additional information.
I did some further tests meanwhile with following results:
1) Output is very same on Windows with very same devices, so it's not an driver issue
2) With another LCD monitor, problem is gone. So it isn't problem of cable nor docking station (at least seems to me)
I'm using Samsung S27D390H (https://www.bhphotovideo.com/c/product/1046838-REG/samsung_s27d390h_27_led_lcd.html). So, if I understand correctly, problem is with my monitor, which can't detect the bit, you have mentioned, therefore I need to buy new one?
(In reply to Ivan Vlk from comment #6)
> 1) Output is very same on Windows with very same devices, so it's not an
> driver issue
So you see the same issue on Windows too?
> 2) With another LCD monitor, problem is gone. So it isn't problem of cable
> nor docking station (at least seems to me)
Are you using the same display mode (resolution) on that other display? The color range setting depends on the mode.
> I'm using Samsung S27D390H
> samsung_s27d390h_27_led_lcd.html). So, if I understand correctly, problem is
> with my monitor, which can't detect the bit, you have mentioned, therefore I
> need to buy new one?
I don't think we have enough information to make that conclusion.
> So you see the same issue on Windows too?
Yes, with the same devices and resolution.
> Are you using the same display mode (resolution) on that other display? The color range setting depends on the mode.
Yes, all is exactly the same, except refresh ration (60Hz vs 60.02Hz).
Please try changing the PC/AV mode, enabling/disabling game mode, and if all else fails, finally resetting all settings on the display.