AMD has submitted Fixed Rate Link (FRL) support for HDMI 2.1 into the open-source AMDGPU driver, targeting the Linux 7.2 merge window. It is worth understanding why this took two years, because the reason points straight at the cable.
What was actually blocked
In February 2024 the HDMI Forum rejected an open-source implementation of HDMI 2.1 from AMD, on the grounds that publishing the code would expose licensed material. That left Linux users on HDMI 2.0 signalling — capped at 18Gbps — while the same hardware ran 48Gbps under Windows. The route eventually found keeps the sensitive parts out of the published driver while still enabling FRL.
What has landed, and what has not, is worth stating precisely:
| Feature | Status | What it enables |
|---|---|---|
| FRL (Fixed Rate Link) | Submitted, compliance tested | Up to 48Gbps — 4K at 120Hz, 5K at 240Hz |
| DSC (Display Stream Compression) | Still in testing | Formats above the uncompressed 48Gbps ceiling |
| VRR (Variable Refresh Rate) | Still in testing | Tear-free variable frame rates |
FRL is a different kind of signal, and cables feel it
HDMI up to version 2.0 used TMDS, in which the clock is transmitted on its own dedicated pair. HDMI 2.1's FRL drops that separate clock, embeds timing in the data, and runs four lanes at a fixed rate up to 12Gbps each — 48Gbps in total. It is closer in character to a modern SerDes link than to the older HDMI signalling.
The practical consequence for anyone buying cable: the margins that TMDS forgave, FRL does not. At 48Gbps the budget for insertion loss, inter-pair skew and impedance discontinuity is far tighter. A cable that has quietly carried 4K at 60Hz for years can fail at 4K120 for reasons invisible from the outside — conductor consistency, dielectric uniformity, shield coverage, and how repeatably the connector is terminated along the whole length.
This is why the HDMI Forum runs a certification programme with a scannable anti-counterfeit label rather than trusting printed claims, and why cables are certified by category — Ultra High Speed, Ultra96 — rather than by a version number.
What to specify if you are building for this
- Ask for the category name, not the version number. "Ultra High Speed" is a certified category; "an HDMI 2.1 cable" is a loose description with no certification behind it.
- Scan the certification label on the packaging. Certified cables carry a holographic label with a QR code.
- Ask which Authorized Testing Centre tested the cable and ask for the report.
- Fix the length early. Passive Ultra High Speed cables are certified up to about 3 m. Past that, specify an active optical cable rather than a longer passive one.
Where our own cables sit
- HDMI A 8K/60 Certified Cable — PF331S — Ultra High Speed, ATC-certified
- HDMI A 4K AOC Cable — PLT288 — active optical, for runs past the passive limit
- All HDMI cables
Ask us for the specification sheet
Tonetron is the export brand of Dongguan Taitron Electronic Limited (东莞台昶电子有限公司), a cable and connector manufacturer in Dongguan, Guangdong, China, established in 1984. We build HDMI, DisplayPort, USB-C and custom cables on our own lines and ship factory-direct to more than 40 countries.
- Email: sales@tonetron.com
- Phone: +86-0769-83356158
- Contact form: tonetron.com/contact
Tell us the target specification, quantity and destination market and we will send the matching datasheet and a quote.
