Pixel clock limited to 165.0 MHz with UHD display on Quadro P400

Graphics / Linux Linux
1

Hello,

I am having an issue where the pixel clock of my UHD display is being limited to 165.0 MHz apparently, and I therefore cannot configure the display to it’s native resolution.

I am using nVidia Quadro P400 GPU with driver 381.22 on Ubuntu 16.04. The display is an LG Ultrawide with only HDMI inputs, so I am using an UHD-compatible active DisplayPort to HDMI adapter (Icybox IB-AC506; as far as I can tell DP v1.2 capable).

This is apparent in the logs (/var/log/Xorg.0.log):

[   285.832] (--) NVIDIA(GPU-0): LG Electronics LG ULTRAWIDE (DFP-5): connected
[   285.833] (--) NVIDIA(GPU-0): LG Electronics LG ULTRAWIDE (DFP-5): Internal TMDS
[   285.833] (--) NVIDIA(GPU-0): LG Electronics LG ULTRAWIDE (DFP-5): 165.0 MHz maximum pixel clock

This is apparent when saving the EDID with nvidia-settings and using parse-edid:

Identifier "LG ULTRAWIDE"
	ModelName "LG ULTRAWIDE"
	VendorName "GSM"
	# Monitor Manufactured week 12 of 2016
	# EDID version 1.3
	# Digital Display
	DisplaySize 670 280
	Gamma 2.20
	Option "DPMS" "true"
	Horizsync 30-90
	VertRefresh 56-75
	# Maximum pixel clock is 240MHz

Why is this so? Is this a software bug? Hardware problem? Is the cable to blame? The adapter?

How do I diagnose this issue?

Any help is much appreciated.

LP,
Jure
nvidia-bug-report.log.gz (144 KB)

2

Please add

Option "ModeDebug" "true"

to the Screen section of your xorg.conf. Then run nvidia-bug-report.sh and attach output file to your post.

3

Attached. Sorry for the delay.

The UHD display is at DP-5, DP-3 is a second display with a lower resolution.

LP,
Jure
nvidia-bug-report.log.gz (144 KB)

4

This line indicates that this is a passive adapter, not an active one:

[    50.381] (--) NVIDIA(GPU-0): LG Electronics LG ULTRAWIDE (DFP-5): Internal TMDS

If it were an active adapter, it would say DisplayPort instead of TMDS. DP-4 (also known as DFP-4) is the DisplayPort partner half of that connector:

DP-4 disconnected (normal left inverted right x axis y axis)
	Identifier: 0x232
	Timestamp:  68779
	Subpixel:   unknown
	Clones:    
	CRTCs:      0 1 2 3
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	CscMatrix: 65536 0 0 0 0 65536 0 0 0 0 65536 0 
	BorderDimensions: 4 
		supported: 4
	Border: 0 0 0 0 
		range: (0, 65535)
	<b>SignalFormat: DisplayPort</b>
		supported: DisplayPort
	ConnectorType: DisplayPort 
	<b>ConnectorNumber: 2</b>
	_ConnectorLocation: 2 
DP-5 connected 1920x1080+1680+0 (0x234) normal (normal left inverted right x axis y axis) 673mm x 284mm
	Identifier: 0x233
	Timestamp:  68779
	Subpixel:   unknown
	Gamma:      1.0:1.0:1.0
	Brightness: 1.0
	Clones:    
	CRTC:       1
	CRTCs:      0 1 2 3
	Transform:  1.000000 0.000000 0.000000
	            0.000000 1.000000 0.000000
	            0.000000 0.000000 1.000000
	           filter: 
	CscMatrix: 65536 0 0 0 0 65536 0 0 0 0 65536 0 
	EDID: 
		00ffffffffffff001e6df159eb7e0100
		0c1a010380431c78eaca95a6554ea126
		0f5054a54b80714f818081c0a9c0b300
		0101010101017e4800e0a0381f404040
		3a00a11c21000018023a801871382d40
		582c4500a11c2100001e000000fc004c
		4720554c545241574944450a000000fd
		00384b1e5a18000a2020202020200125
		02031cf1499004031412051f01132309
		07078301000065030c001000023a8018
		71382d40582c450056512100001e011d
		8018711c1620582c250056512100009e
		011d007251d01e206e28550056512100
		001e8c0ad08a20e02d10103e96005651
		21000018000000ff003631324e544641
		32573032370a000000000000000000af
	BorderDimensions: 4 
		supported: 4
	Border: 0 0 0 0 
		range: (0, 65535)
	<b>SignalFormat: TMDS</b> 
		supported: TMDS
	ConnectorType: DisplayPort 
	<b>ConnectorNumber: 2</b> 
	_ConnectorLocation: 2 
  1920x1080 (0x234) 148.500MHz +HSync +VSync *current +preferred
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
5

Given that the adapter I have (Icybox IB-AC506) is advertised as active, how do I recognize an actual active adapter pre-purchase?

LP,
Jure

6

I’m not sure you can just from looking at it. The only foolproof way I know of is to plug it in and check Xorg.0.log or xrandr --verbose.

7

Looking at the specs of your adapter, it says 4k@30Hz. Which is not what I would expect from an active HDMI 2.0 adapter. Should be 4k@60Hz then.

8

I never thanked you guys. That was it.

My issue was that the reseller I was using neglected to include the @30Hz bit in their product specification and the result was confusion.

I’ve alerted them to the issue and brought a different adapter that can do UHD @60Hz and it works flawlessly.

LP,
Jure

9

Which did you buy that worked?

10

Delock 62735:
[url]Delock Products 62735 Delock Adapter mini DisplayPort 1.2 male > HDMI female 4K 60 Hz Active