Can't get 4K 120Hz with i7-13620H and ThunderBolt 4 Port

[Nablista]

Hello,

I bought a Dell Inspiron 16 Plus 7640, which comes with an i7-13620H (Intel 13th generation) with iGPU UHD 620.

It is connected to my LG G5 TV with this cable "USB C HDMI 2.1, 4K@240Hz" (Cable Matters) from the ThunderBolt 4 Port of the laptop to the HDMI 2.1 of the TV.

The problem I encounter :
- I am able to select the 4K Resolution, but when selecting the 120Hz, I get a blackscreen on the TV, then "No Signal" message and after 10 second the refresh rate automatically reverts to 60Hz and the screen resume on the TV.
- 120Hz works at 2560x1440 or 1920x1080, with or without HDR/10bits. It's only at 3840x2160 that it doesn't.

What I already done / tried :
- I tried with another dell laptop that comes with an i5-1245U (with Xe Iris iGPU) and it works well (4K 120Hz), so the USBC -> HMDI 2.1 cable is not the problem
- The LG TV is in HDMI Deep Color 4K mode
- Tried all 4 HDMI 2.1 ports of the TV, and verified that it was using the good one.
- Tried disabling HDR or reverting to 8bits but it doesn't allow 120Hz either
- Firmware are up to date, both for CPU/GPU (downloaded directly from intel website), BIOS and TV.
- I tried with only the TV active (not my internal display)
- I disabled all "Power Savings" parameters
- Dell locks DSC on some of its models. I tried following their tutorial (https://www.dell.com/support/kbdoc/en-us/000197102/how-to-enable-display-stream-compression-on-latitude-precision-and-xps) to force it, but my model doesn't have the DpMstDscDisable key in the registry, so my model should not be concerned
- I tried running Cable Matters firmware update (https://kb.cablematters.com/index.php?View=entry&EntryID=147)

[VonM_Intel]

Hi Nablista,

Thank you for posting in our Community. At this point, the behavior you’re seeing appears to be related to a limitation or configuration constraint with the i7-13620H and UHD Graphics on the Inspiron 7640, rather than the cable or the TV. I understand that you have a laptop. Since this is an OEM (Dell Inspiron 16 Plus 7640) original equipment manufacturer device, please take into consideration that our support may be limited since we are not familiar with the technology, settings, customizations, custom drivers, and features that the OEM has designed and installed your system, nevertheless, I will do my best to assist you with your concern. To help dial things in further, let me ask a few quick questions so I can confirm:

• When you plug in the TV, does Windows detect the connection as DP, HDMI 2.1 or as HDMI 2.0?
• What’s the exact model of your LG G5 TV? Some sub-models split HDMI bandwidth differently across ports.
• If you open the Intel “Advanced Display” page, what’s the max reported bandwidth or link rate? This will tell us if the laptop is even negotiating enough lanes.
• Can you share the exact Intel Graphics driver version installed the Intel SSU logs, as this will enable me to collect detailed information about your system setup, which could aid in identifying the underlying cause of this issue.

Have a nice day!

Best regards,

Von M.
Intel Customer Support Technician

[Nablista]

Hi VonM,

Thanks for your answer.

• The only place where I could find the information was in the Intel Graphics Command Center app. It says "Connector Type : DiplayPort". Just below the screenshot of what I see, with all supported modes.
  
• The TV is an OLED48G56LS
• In the Advanced Display, I can select up to 120Hz.
  When I select the 120Hz, I get a BlackScreen on the TV, followed by a "No Signal". After 10 seconds, it reverts to 60Hz.
  Below a screnshot of the "Advanced Display" pannel + graphic card property + valid modes
• Please find attached the SSU logs. I run it with only the TV as active screen in 4K @60Hz with HDR/10bits, just after trying to switch to 120Hz.
  The GPU driver installed is 32.0.101.7080

Best Regards,
Nablista

[Nablista]

The second screenshot was not uplodaded. Please find it attached.

[MUC]

What happens if you select 100 Hz?

[Nablista]

Exactly the same issue

[TheExpertGuy]

...Aight, so the i7-13620H’s integrated graphics (UHD 620 / 13th Gen Intel) straight up might not be able to push 4K 120Hz over a single USB-C/DP 1.4 link without DSC. Some Intel chips gotta have Display Stream Compression (DSC) to hit 4K 120Hz over USB-C/HDMI. On top of that, Dell might’ve locked it down in the BIOS/firmware, so you can’t force DSC (like you saw, no DpMstDscDisable key). That Cable Matters cable saying 4K@240Hz? Doesn’t matter here  > the bottleneck’s the iGPU, not the cable. If you got a full-size DisplayPort or miniDP on your Dell, or a dock with DP outputs, give that a shot. DP 1.4 plus DSC might actually push 4K 120Hz smoothly. Lower res like 1440p or 1080p at 120Hz works fine ‘cause it needs less bandwidth. If you really wanna hit 4K120Hz, a DP 1.4 dock is probably your best bet.

[Nablista]

Interesting.

• Do you have an idea on how I can check if Dell has locked it down in the BIOS/firmware ?
• Unfortunately I only have a HDMI 1.4 port...
• For the dock there is something I don't get. Let's say Dell has locked DSC features and I use a Dock.
  Would the dock do the DSC itself ?
  Even if it was the case, my computer wouldn't be able to send 4K 120Hz (as DSC would be locked in my computer) to the dock no ?

[MUC]

The bandwidth required for a video signal does not depend on the graphics card manufacturer. It depends on the video timing required by the display and other parameters.

Video Timing:

For TVs, there is only one video signal for 4K @ 120 Hz, and it is always the same. It corresponds to the video timing according to CTA-861 (CTA = Consumer Technology Association) with a pixel clock of 1188 MHz.

Other Paramters:

Color model and color depth influence the bandwidth required for signal transmission.

(1) 4K @ 120 Hz RGB 10-bit = 40 Gbps (HDMI 2.1 Fixed Rate Link 5).

(2) 4K @ 120 Hz RGB 8-bit = 32 Gbps (FRL4)

(3) 4K @ 120 Hz YCbCr 4:2:0 8-bit = 18 Gbps (594 MHz TMDS = HDMI 2.0)

The mentioned Cable Matters product (USB Type-C > HDMI 2.1) with an Intel NUC11 from 2021 (Thunderbolt 4) looks like this when transmitting signal (1):

To output signal (1), the source must support DSC. A docking station offers no advantage; rather, it increases the risk that it can only use two lanes for video transmission, which would halve the available bandwidth.

Theoretically, no DSC is needed to output (2) or (3). Color depth and color model can be set via the Intel Graphics Software.

However, since @Nablista has already tried all of this and isn't getting a usable signal, I would address the issue with Dell Support. There appears to be an incompatibility between the Inspiron 16 Plus 7640 and the Synaptics VMM7100 PCON chip used by Cable Matters. As an integrator of Intel components and a system designer, Dell is ultimately responsible for the overall system's behavior. As an Original Equipment Manufacturer (OEM), they are also responsible for providing any necessary adapted firmware or drivers for their systems.

[Nablista]

Thanks a lot for the deep explanation.

I asked Dell support and below is their answer. Could you give me your opinion on it ?

• I understood that the i7-13620H with UHD 620 iGPU have 1500 MHz of Graphics Max Dynamic Frequency, so it should be able to handle the 1188 MHz required for 4K @120Hz, right?
• The other computer I tested doesn't have a discrete graphic card but it works at 4K @120Hz, so I don't understand their explanation with discrete GPU...
• Regarding the "nor do the specs indicate so" that's sometingI don't  understand neither.
  On the intel i7-13620H spec page it is written that "Max Resolution (DP)‡ : 7680 x 4320 @ 60Hz", and I think that is what they are referring to.
  But if it was locked at 60Hz, I would not be able to display at 1920 x 1080 @ 120Hz right ?
  Also the other computer (i5-1245U) has the same display specs...

Below a screenshot of what I have on VmmDpTool64 @60Hz :



And @120Hz (but nothing show on the TV, I have a "No Signal" message) :

[MUC]

Perhaps the problem is also related to the fact that the Intel display engine changed starting with the 13th gen processors.

In any case, this would be a reason for Dell/Intel/Synaptics to review this interface.

Synaptics Spyder VMM7100

Works seamlessly with the latest USB4 and Thunderbolt notebooks

Certified by Intel for use on the latest Alder Lake CPU & Alchemist (DG2) GPU platforms based on the Xe-HPG architecture
Selected by Intel for Alchemist (DG2) reference validation platforms (FRD7)

---

[MUC]

Ah, interesting. So the VmmDpTool64 status indicates that everything up to the TV's HDMI input is working perfectly. Then there might be a problem with the LG G5's firmware. That's a tricky case.

That changes things somewhat, because based on this data, Dell/Intel/Synaptics will rightly claim that everything is fine on their end. You definitely don't need a dedicated graphics card for 4K @ 120 Hz. It also works with the integrated GPU via the DisplayPort HBR3 protocol, as you can see in the diagnostic status:
RX SST 4lane HBR3 mode

• RX = Receiver
• SST = Single Stream Transport
• 4 lanes (as it should be)
• HBR3 = High Bit Rate 3, which corresponds to the DisplayPort 1.4a specification. The processor also supports this. Just like my 11th gen processor in a NUC device that's already four years old. I also successfully tested 8K @ 60 Hz YCbCr 4:2:0 8-bit, which corresponds to a bandwidth of 32 Gbps and a pixel clock of 2376 MHz.
• DSC ON
• FEC (Forward Error Correction) enabled

This is a valid video link.

4K @ 60 Hz RGB 8-bit (CTA-861) = 594 MHz TMDS

1080p @ 120 Hz RGB 8-bit (CTA-861) = 297 MHz TMDS

The refresh rate itself is not the limiting factor. There seems to be a problem with the TVs firmware, as the VmmDpTool64 status indicates successful HDMI sync @ FRL4.

Please contact LG support. Unfortunately, a precise analysis would require diagnostic hardware.

[Nablista]

But what is strange from my understanding is that with my other dell computer (that also have an iGPU) I don't have at all this problem. I plug the cable and it works at 4K 120Hz.

How can it be a LG TV firmware problem in this case ? This synaptic chip is sending exactly the same signal no ?

[MUC]

The Synaptics chip actually sends exactly the same signal, yes.

This is apparently a compatibility issue. In such cases, it's always difficult to pinpoint the exact culprit. I don't expect a concrete answer from LG, but contacting them will bring the problem to the attention of their support team. Perhaps they'll discover a hidden bug and fix it with the next firmware update.

In my opinion, connecting a Thunderbolt laptop to a 4K TV at 120 Hz is a fairly common use case. I do it myself with my NUC on an LG G3. Therefore, it would be good if every company involved in the technical aspects reconsidered this.

[Nablista]

Also thanks to have confirm it is not an iGPU problem. I found very odd that the dell support answered me that it was the cause.

I just found something very disturbing. I just played (again) with the 8 / 10 / 12 bits in the intel software, and with the 60 /100 /120 Hz in the Intel Command Center (Beta).
For a reason I can't understand, it worked : I was able to stream 4K @120Hz 10 bits RGB with HDR. I had to wait few seconds for the "No Signal" to disappear and show the screen. It was in "Extend view", so my internal screen was displaying as well. I switched to "Only 2nd screen" (The TV), and it wasn't working anymore (Black screen).

I disconnected and reconnected the cable but it wasn't working anymore. Tried 5 more times (playing witch bitrate and framerate)

I need to do some more backtesting, as I can't reproduce as well the VmmDoTool64 log @120Hz...

I'll keep you updated with what I find, and try to understand it it's purely random or if there is pattern that could help understanding what is happening.

[Nablista]

Hey @MUC,

I have been trying for over a month to find a solution to my problem, without success.
If you have some time, I would be interested in your opinion on a subject.

I contacted LG support without success for now.

I discovered something quite strange:
When I select 4K 120Hz 10bpc RGB, it rarely works the first time, and I get a “No Signal” message.
Usually, after launching VmDpTool and pressing “Reset Board,” it works, but the VMM 7100 downgrades the signal to 8bpc (I checked on the TV, and it is receiving an 8bpc signal):

 

However, when I test in 4K 60Hz 10bpc RGB, the 10bpc does reach the TV (so the TV can handle 10bpc):

The other thing I discovered is that if I select 4K 120Hz 8bpc 4:2:0, it works instantly (without needing to “Reset Board.” The operating mode is FRL 3L6).

It's also the same in 4K 60Hz 10bpc RGB (FRL 4L6).

The only modes that don't usually work on the first try are all FRL 4L8 modes (4K 120/120Hz 8bpc RGB/4:2:2/4:4:4), where I sometimes have to “Reset Board” several times before it works.

My theory: for some reason I don't know (the chip? the TV? an incompatibility?), the chip can't send 4K 120Hz 10bpc RGB in FRL 4L10/12, and downgrades to 8pbc to make it work.

I contacted Cable Matters about this, and they thought it was the cable that was defective. They sent me another one (same model) and it still doesn't work. I've tried all the available software, and they all work the same way.

Any ideas on what I can do to try to get this working?
Test another cable that doesn't use a VMM 7100?

[MUC]

Thank you for the interesting details. Unfortunately, I don't have any brilliant ideas at the moment either.

Contacting Cable Matters was definitely the right thing to do. After all, they have a strong interest in compatibility.

You could also try this product:

UGREEN USB Type-C > HDMI 2.1 FRL cable

As far as I know, the UGREEN Protocol Converter products are based on the Chrontel CH7218A chip. I haven't tested it myself yet.

The functionality is said to be good, however, the HDMI plug (in which the chip is integrated) is said to get somewhat warm.