4K resolution can't be selected on monitor connected via HDMI to Thinkpads with Intel CPU and GPU

[Robert-CH]

This is a question about a problem apparently confined to Thinkpads with Intel components. Lenovo Support (Germany) have drawn a blank, and I'm wondering if someone knowledgeable about Intel hardware and/or drivers might have an opinion about the cause.

When I connect a Lenovo T34w (34-inch, curved, manuf. Oct 2024) monitor to my Lenovo T15 Gen2 Thinkpad (type 20W4-008MMZ) via its HDMI port, the maximum resolution Windows allows me to select for the monitor is 2560x1080@60Hz. When instead the monitor is connected via USB-C (or DisplayPort via a USB-C dock), 3440x1440@60Hz is selectable. Lenovo Support confirm that failure to provide 3440x1440 via HDMI is a defect: the specs for both monitor and T15Gen2 say it should be possible.

When I write "the problem" in following paragraphs I mean this phenomenon that only 2560x1080@60Hz is selectable instead of the expected 3440x1440@60Hz when a T34w monitor is directly connected via HDMI to one of several Thinkpads.

My T15Gen2 (type 20W4-008MMZ) has the following Intel components:
Processor: Intel Core i7-1165G7 (4C / 8T, 2.8 / 4.7GHz, 12MB)
Graphics: Integrated Intel Iris Xe Graphics functions as UHD Graphics
OS: Windows 10 Pro 64-bit.

The problem also occurs with two older Intel Thinkpads whose User Guides say an external monitor connected via HDMI can achieve up to 4096x2160 (Hz not mentioned). When the T34w is connected to either of these only a maximum of 2560x1080@60Hz is selectable. These two Thinkpads are:

Thinkpad X260 type 20F5-S74700
Processor: Intel i5-6300U
Graphics: Intel Graphics 520
Windows 10 Pro 64-bit (22H2 19045.3324)

Thinkpad E560, type 20EV-0000XMZ
Processor: Intel i7-6500U
Graphics: Intel HD Graphics 520 and AMD Radeon R7 M370
Windows 7 Pro 64-bit SP1

The problem does NOT occur with a new AMD E16Gen2 Thinkpad. When the T34w is connected to this device via HDMI 3440x1440@60Hz is selectable. Specs for this laptop are:

E16 Gen2 Thinkpad, type 21M5-S02E00
Processor: AMD Ryzen 5 753U
Graphics: AMD Radeon Graphics
Windows 10 Pro 64-bit

To summarise: The problem occurs in apparently the same way under Windows on three Intel Thinkpads, but not on an AMD Thinkpad.

The problem does not occur on the T15Gen2 when the T34w is connected to it via a Lenovo Universal USB-C Dock (40AY0135CH) – i.e. dock connected to Thinkpad via USB-C, monitor connected to dock via HDMI. Here, surprisingly, 3440x1440@60Hz is selectable.

The problem apparently occurs only under Windows (10 or 7). It does not occur on the T15Gen2 under Ubuntu (tried out on a flash drive). Under Ubuntu 3440x1440@60Hz is supported.

I actually have two identical T34w monitors. Both behave identically in all tests. Both have the latest firmware (v. 1.06).

The HDMI cable used when the problem occurs is the same one used when the problem does not occur (with dock or under Ubuntu). In fact all tests have produced the same results with two different cables: the official Lenovo cable (0B47070, bandwidth 10.2 Gbit/s) and a non-Lenovo cable from Amazon (Soonsoonic 4K@60Hz HDMI cable, 18Gbps Ultra High Speed HDMI 2.0).

Lenovo Support have so far only concerned themselves with the T15Gen2 (the X260 and E560 are too old to interest them). Remedial measures tried so far by Lenovo Support have been to: (1) upgrade the firmware in the slightly older monitor from 1.05 to 1.06; (2) reinstall the latest Windows graphics driver (32.0.101.6647); (3) replace the motherboard in the T15Gen2; (4) have me reinstall Win 10 Pro 64-bit on the T15Gen2. None of these have had any effect on the problem.

To finally get to the point of this post: does anyone knowledgeable about Intel hardware and drivers see any possible explanation of the problem? I am myself not knowledgeable enough to know if the likely culprit is Windows, drivers, or monitor firmware.

I'm also not sure what screenshots etc. might be useful. I'll gladly attach more on request.

[MUC · Accepted solution]

The official Lenovo Product Specifications Reference (PSREF) states the following:

Monitor ThinkVision T34w-30

3440 x 1440 @ 60 Hz RGB 8-bit

1 x HDMI TMDS

1 x DisplayPort HBR2

1 x USB Type-C DisplayPort Alternate Mode

EDID:

00 ff ff ff ff ff ff 00 30 ae f3 61 56 56 47 47

0e 1e 01 03 80 50 21 78 ee 62 f5 aa 52 4c a3 26

0f 50 54 a1 08 00 81 00 81 80 95 00 81 c0 b3 00

d1 c0 01 01 01 01 e7 7c 70 a0 d0 a0 29 50 30 20

3a 00 1d 4e 31 00 00 1a 00 00 00 ff 00 56 33 30

35 47 47 56 56 0a 20 20 20 20 00 00 00 fd 00 30

64 1e 94 37 00 0a 20 20 20 20 20 20 00 00 00 fc

00 4c 45 4e 20 54 33 34 77 2d 32 30 0a 20 01 37

02 03 2f f1 52 01 03 04 13 1f 12 02 11 90 0f 0e

1d 1e 05 14 4b 4c 5a 23 09 07 07 83 01 00 00 67

03 0c 00 10 00 00 42 67 d8 5d c4 01 78 80 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 59

ThinkPad T15 Gen 2

2 x Thunderbolt 4 (DisplayPort HBR3)

1 x HDMI TMDS

ThinkPad X260 (Skylake)

1 x mini DisplayPort HBR2

1 x HDMI 1.4 (4096 x 2160 @ 24Hz)

ThinkPad E560 (Skylake)

1 x HDMI 1.4 (1920 x 1080 @ 60Hz)

ThinkPad E16 Gen 2 (AMD)

AMD Ryzen 5 7535U

1 x HDMI TMDS (4K @ 60 Hz)

1 x USB Type-C (USB 10 Gbps) supports up to 5K @ 60Hz

1 x USB Type-C (USB 5 Gbps) supports up to 4K @ 60Hz

My explanation: The devices in question do not support HDMI output resolutions at the driver level that are not included in the Consumer Technology Association (CTA) specification. HDMI is essentially a consumer electronics interface specified for televisions and similar devices. Compatibility with ultrawide displays is limited if only CTA-861 video timing is supported.

2560 x 1080 is included in CTA-861, but 3440 x 1440 is not.

Lenovo usually has the final say on what the HDMI port should support, so I'm surprised they don't have an answer on this. However, it is generally true that HDMI ports on Intel devices are usually limited to CTA-861 video timing and do not output signals that deviate from it, despite Detailed Timing Descriptors (DTDs) in the EDID.

The monitor specifies:

This is the video timing for "PC signals" to monitors defined by the Video Electronics Standards Association (VESA) in Coordinated Video Timing – Reduced Blanking (CVT-RB). Apparently, your Intel devices can't output this via HDMI. There's no technical reason why this shouldn't work, but it seems to be a common issue with Intel. If this signal is sent from the laptop to the docking station and converted to HDMI there, it works. This makes sense because the Intel driver then only supports the DisplayPort protocol, as if a monitor with DisplayPort were connected. The docking station's HDMI functions are then independent of the Intel driver's behavior regarding HDMI.

AMD devices and Nvidia graphics cards seem to have no qualms about outputting non-TV signals via HDMI. I've been wondering for a while why Intel devices behave this way, but it happens regularly.

Just to be clear: It's not the bandwidth that's causing the issue.

3440 x 1440 @ 60 Hz RGB 8-bit (CVT-RB) = 320 MHz pixel clock

3840 x 2160 @ 60 Hz RGB 8-bit (CTA-861) = 594 MHz pixel clock

[Robert-CH]

@MUC I have just one question: is this problem fixable? Could it be fixed with an update to the (Windows) driver, or is it something hardwired into hardware components? By which I mean: is there any conceivable way Lenovo could issue a fix for the problem?

Thank you.

EDIT: I've just remembered that under Ubuntu on the T15Gen2 the T34w-30 achieves 3440x1440@60Hz via HDMI. Since the hardware is the same I assume the difference from Windows must lie in the driver. Does that mean that in principle the Windows Intel driver could be modified to support 3440x1440 over HDMI?

[Robert-CH]

@MUC In case it's of interest, I got https://people.freedesktop.org/~imirkin/edid-decode/  to decode the Window registry's hex dump of the EDID of a T34w-30 monitor connected via HDMI to the T15Gen2:

The upper limits in the second-last line are smaller than you got for your T34w-20, particularly the clock. If smaller means worse, that's consistent with my impression of the relative merits of the two models.

(When the monitor is connected via USB-C all the numbers are the same. The only difference is that "(GTF)" is replaced by "(Bare Limits)".)

[MUC]

Yes, in my opinion, this is a software-fixable issue on the T15 Gen 2. As your screenshot confirms, all T34W monitors appear to have a maximum of 3440 x 1440 @ 60 Hz RGB 8-bit with CVT-RB. This corresponds to a pixel clock of just under 320 MHz, which is unaffected by the range limits. The T34W features HDMI 2.0 TMDS, which allows pixel clock speeds of up to 600 MHz.

3440 x 1440 @ 60 Hz RGB 8-bit (CVT-RB) = 53% of HDMI 2.0 bandwidth

Please also see: https://tomverbeure.github.io/video_timings_calculator

If the Lenovo Windows driver wanted to output this via HDMI, it should be possible with the T15 Gen 2. The Iris Xe in the Core i7-1165G7 has a display engine capable of outputting 600 MHz TMDS. Lenovo also specifies "HDMI 2.0" and "4K @ 60 Hz" for the interface. 4K @ 60 Hz = 594 MHz TMDS. Whether Lenovo can be persuaded to address the graphics driver is, of course, another question. The official Lenovo driver is this one.

However, it wouldn't work with Skylake devices, as HDMI 1.4 implementations on Intel processors support a maximum pixel clock of 300 MHz. This is a hardware limitation.

[Robert-CH]

Again, many thanks. You've taught me a lot.

That Intel graphics driver (32.0.101.6647) is the one I have installed on the T15Gen2 and did all my testing with.

My two Skylake devices are quite old and not a primary concern. I merely tested the T34w on them to try to convince Lenovo Support that the problem lay in the Intel drivers, and that motherboard swaps and Windows reinstallations were not going to help.

Lenovo also regard the T15Gen2 (it is a Windows 10 machine) as outdated and can't be expected to make a driver fix from which only an old model would benefit. I suppose it will come down to the reputation of their top-of-the-line monitor and how many customers are connecting T34s to more recent Intel Thinkpads and seeing the problem. I'm going to show Lenovo Support what you've written here and hopefully it will convince them to take the issue seriously.

[Robert-CH]

@MUC Many many thanks for this analysis. It comes as salvation after weeks of blundering in the dark, and I am really grateful for the trouble you've taken. Your explanation seems to me (a mere software engineer) unassailable.

I omitted to mention that my two monitors are both T34w-30 models, whereas the one you used to dump the EDID is a T34w-20. I don't think it makes the least bit of difference to your conclusions, but for the record here is the EDID from one of mine (hex from the registry, and then dumped by the NirSoft dumpEDID utility, which is not as sophisticated as the one you used):

It surprises me too that Lenovo L2 Support didn't know that their top-of-the-line monitor fails to perform to specification, or why this should be the case. I am in Switzerland and get support from Lenovo in Germany, which I suppose is considered a remote outpost from the perspective of China and the USA. The support people in Germany are very professional but, from what I was told, under-resourced. They have no T34w monitor to test with, and no T15Gen2 either. It was for lack of a simple lab test on the right equipment that we went through unfruitful steps like swapping the motherboard and reinstalling Windows.

You are well off with your T34w-20. The T34w-30 seems to have been a rushed job and is a step backwards. An unusable little joystick on the back of the monitor has replaced the former front buttons for adjusting monitor settings on screen, the user guide is a half-finished mess (ignores the existence of new features like the joystick), and one of my pair has a broken USB port which will probably justify sending it back.

Anyway, thanks again for your expert help.

[Robert-CH]

Ignore this post.

[Robert-CH]

For the record, some minor corrections/additions to the original problem description.

Version numbers for the T34w firmware should be 1.5 and 1.6 (not 1.05 and 1.06).

Both the X260 and E560 achieve 3440x1440@60Hz when the T34w-30 monitor is connected via DisplayPort: the X260 directly, using its mini-DP port; and the E560 indirectly via a OneLink dock.

[Robert-CH]

For the record, some more information relevant to the problem.

(1) I attached a T34w-30 monitor to the HDMI port of a new Intel ThinkPad X1 Carbon Gen 13 Aura Edition, type 21NS0010MZ. The problem did not occur: a resolution of 3440x1440 was selectable. The graphics driver on this model is described in the DeviceManager as "Intel Arc 140V GPU (16MB)". Maybe newer Intel drivers don't exhibit the problem.

(2) The Lenovo T34w-30 monitor comes with a driver. The User Guide tells you where to fetch this driver (here) and how to install it. Quite a few of my tests on the T15Gen2 were done without this driver installed. I have now repeated all the tests involving HDMI and verified that installing the driver makes no difference to any of them. In fact the T34w-30 in general seems to work perfectly well without this driver being installed, and it was not installed on any of Thinkpads I tested apart from the T15Gen2.

The driver can only be installed when the T34w-30 is connected to the laptop. Before it is installed the monitor is represented in the Device Manager by an entry in the Monitors section with the name "Generic PnP Monitor". You install the driver by running "Update Driver" on this entry, after which the entry has the name "T34w-30". It's a fairly small driver and I think it is part of the "ThinkColour software" described in the Lenovo sales literature. The installation adds configuration data to the Windows registry like the samples attached.