FPS capped to 60

[pazkaw]

I recently picked up a new 4k 120 fps monitor (Dell S2725QC), but for some reason, my Surface Laptop 5 (i7-1265U processor with Iris Xe) remains stuck at 60 fps. I'm connected to the monitor through a USB-C with DP cable that came in the box, which should be capable of supporting 4k @120fps.

I've updated the graphics drivers to the latest version, tried reinstalling them, rolled them back to a previous version and start all over again, but no luck. I also ran the Intel DDU utility in safe mode followed by a fresh driver installation. 

After each fresh driver installation, the 120Hz refresh rate initially shows up in the dropdown box of Window's "advanced display" options as well as under the monitor's "all modes" options. But when I try to apply it, the monitor immediately reverts to 60Hz and the 120Hz option disappears again from the menu. This seems a little strange as AFAIK my hardware should be capable of supporting 4k @ 120 fps, but I might be mistaken.

I've also tried to add a 'detailed resolution' manually in CRU, but the OK button greys out when I enter 4k @ 120fps. Finally, I've also fiddled with a bunch of settings in Intel Graphics Command Center (like turning off HDR and switching from RGB to YCBCR) but no dice. 

I'm attaching Intel's SSU report for your reference. Many thanks for your help!

[AlphaTop89]

hi, The Intel Iris Xe Graphics on the Surface Laptop 5 doesn't officially support 4K @ 120Hz output. The limitation isn’t your monitor, cable, or even driver. It’s likely a hardware bottleneck specifically, the DisplayPort (or USB-C/Thunderbolt) output bandwidth of the laptop. The USB-C port on the Surface Laptop 5 supports USB 4 / Thunderbolt 4, which theoretically can carry DisplayPort 1.4 HBR3 signals (enough for 4K @ 120Hz) But in reality, the Intel Iris Xe graphics limits the actual throughput, and OEMs (like Microsoft) can limit this via firmware or power/bandwidth-sharing constraints. Most likely, the output is restricted to DP 1.2 bandwidth, which supports 4K @ 60Hz max. Intel’s Iris Xe Graphics (on mobile U-series CPUs) are only guaranteed to support one 4K @ 60Hz display natively. Pushing 4K @ 120Hz requires DSC (Display Stream Compression), which is not reliably implemented on all OEM devices or drivers. When CRU greys out the “OK” button for 4K @ 120Hz, it’s a sign that the EDID data from the laptop GPU doesn’t support it. Use Intel Graphics Command Center > Display > Monitor Details to check what DP version is active. If it’s stuck on DP 1.2, that’s your bottleneck. Set your display to 2560x1440 @ 120Hz to see if it applies. If this works, it confirms your GPU and port can do 120Hz, but not at 4K. 

• If you absolutely need 4K @ 120Hz from your Surface, the only real workaround is using an eGPU setup via Thunderbolt 4 or:

  • A USB-C dock with DSC support and an HDMI 2.1 port.

  • (Something like the Plugable TBT4-UDZ or CalDigit TS4 might help, though it's a pricey workaround.)

[MUC]

According to the Dell S2725QC user manual, the monitor supports DisplayPort Alternate Mode at 4K @ 120 Hz (likely 4-lane HBR3 without DSC) over USB Type-C.

According to the diagnostic data, the monitor explicitly does not support YCbCr 4:2:0, which is not recommended for use as a computer monitor anyway. While the listed modes do not include 4K @ 120 Hz, the EDID itself advertises VIC #118, which corresponds to the UHD TV standard. However, this standard (CTA-861) would require 110% bandwidth over DisplayPort 1.4 HBR3 without DSC and is therefore not possible. Only over HDMI FRL5, which the monitor supports according to the user manual.

To analyze the full EDID of the monitor, please run edid-test.exe:

https://www.monitortests.com/edid-test.zip

This will create a file named "edid-test.txt" in the same folder. Please attach this TXT file here.

[pazkaw]

Thank you both for your extensive replies! 

@AlphaTop89 that seems plausible. I'm able to run my display at 2560x1440 @ 120Hz just fine. The Display Info in Intel Graphics Software tells me it's connected through "DisplayPort", but doesn't tell me which version. I've tried looking elsewhere, but it doesn't seem so easy to find. Do you know another way of checking?

@MUC According to intel's command center, the display is currently connected through RGB rather than YCBCr so hopefully that won't cause any problems. But the bandwidth limitations definitely sound plausible. Do you think that connecting the monitor through HDMI might theoretically resolve the issue? My Surface laptop doesn't have an HDMI port, so the only option would be to connect the HDMI through a docking station - but I reckon that would pretty much throttle the bandwidth back again to its current speed over Displayport. 

[MUC · Accepted solution]

EDID-test.txt shows the third part of the EDID, which is unfortunately not correctly captured by the Intel graphics driver report:

The yellow area indicates the parameters the monitor expects for 4K @ 120 Hz.
This corresponds to the CTA-861 (UHDTV) standard. This signal cannot be transmitted via the DisplayPort 1.4a HBR3 protocol without DSC. This confirms the theory above.

For 4K @ 120 Hz, you'll need to use the HDMI port on your monitor. To connect your Surface Laptop accordingly, you have the following options:

1. [Designed for Surface] Cable Matters 48Gbps USB-C to HDMI Cable (201562)
2. [Designed for Surface] Cable Matters USB-C to 8K HDMI Adapter (201588)

If you decide to use the adapter, please note that interference-free transmission of bandwidth-intensive signals is only guaranteed with (certified) "Ultra High Speed" HDMI cables up to 3 m (10 ft) in length.

These products contain the Synaptics VMM7100 Protocol Converter (PCON) chip. The Surface Laptop will send [DisplayPort HBR3+DSC] to the chip, which then decompresses this to 4K @ 120 Hz RGB 10 bpc Fixed Rate Link 5 (40 Gbps) for transmission to the monitor.

I myself use one of these VMM7100 products from Cable Matters with a NUC11, and it works perfectly on the TV.

[MUC]

I found this section in the monitor's manual.

So the monitor does indeed support DSC and can therefore also be connected via USB Type-C. Nowhere in the manual does it mention the need to separately enable DSC or anything like that. Why this doesn't work for you at the highest resolution is hard to say. However, the workaround with the Cable Matters adapter is probably the easiest if you absolutely need 4K @ 120 Hz. If you value the ability to charge via USB Type-C, you'll have to lower the resolution or refresh rate.

It may also be helpful to submit a support request to Dell. There may be a firmware update for the monitor.

[pazkaw]

Thank you very much indeed! I'm traveling at the moment but I'm tempted to grab myself one of those Cable Matters adaptors as soon as I get back. If I do I'll report back to the community whether that's resolved the issue. Filing a support request with Dell is probably a good idea too.