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Work · Qualcomm · Boulder · within Oct 2009 – Jan 2022 · Linux kernel contributor
While at Qualcomm, contributed a Linux kernel module supporting HDMI output with hardware encryption for MSM-family SoCs. HDMI carries the visible signal; HDCP — High-bandwidth Digital Content Protection — encrypts it in hardware so a downstream display can prove it is licensed to receive it. The driver glues the chip's cipher engine, key ladder, cable-state machine, and the upstream DRM/KMS surface into one kernel module that exposes the secure display path to userspace cleanly. References live upstream in the Linux kernel git history with the contributor's name on them.
git log --author="Urs Muff" — see the mainline tree and the kernel mailing-list archive.tend / attune / compost / release). Different naming, same posture.Why this work matters in the body of evidence
The kernel work is the only piece in the body of evidence with a public, attributed, immutable trace. Quark and MindTouch and Trimble source code lives behind corporate walls; the BML thesis archive is local to this repo. But Linux kernel commits are signed-off by author, reviewed in public on the kernel mailing list, and merged into a tree that is mirrored across thousands of machines worldwide. A contribution to that tree carries the engineer's name into a corner of the commons that won't be edited away.
HDMI looks simple from a userspace perspective: plug in a cable, the screen lights up. From the kernel's perspective, the path from a frame in memory to pixels on a remote display crosses five separate hardware blocks, each with its own clock domain, its own register set, and its own failure mode. The driver is what coordinates them.
What HDCP actually does
HDCP is a key-ladder authentication protocol with in-line stream encryption. The first second of the link is spent in authentication: source and sink exchange public values, derive a shared session key from a key ladder rooted in device-specific secrets, and prove to each other that neither has been revoked. Once authenticated, the cipher engine in hardware uses the session key to scramble every TMDS pixel before it goes on the cable. The sink unscrambles in hardware on the other end. From the application's perspective the picture looks identical; what changed is that an unauthorised recorder on the cable can't reconstruct the frames.
The driver's job in this is delicate. The cipher engine is fast but the link-integrity verification — the periodic check that the same key is still in effect at both ends — has to fire at very specific points in the video frame. A late check kills the picture (the sink falls back to a blank screen with "encryption error"); a missed check opens an audit hole. The kernel module times these actions against the video clock, kicks the hardware, collects the verification result, and either continues silently or tears the link down and re-authenticates. All without dropping frames userspace can see.
Most of this body's work lives behind corporate walls. QuarkXPress source is internal. MindTouch source is internal. Trimble source is internal. The Qualcomm test harness ran on internal infrastructure. Even the BML thesis archive lives on a personal machine. None of that work has a public, attributed, immutable record outside the company that owned it.
The Linux kernel is different. Every commit is Signed-off-by: its author. Every change is reviewed publicly on the kernel mailing list, archived at lore.kernel.org, and merged into a tree mirrored to every machine that runs Linux. A contribution to that tree is forever- attributed to its author in a way no corporate codebase can match. To find this body's contributions, run git log --author="Urs Muff" in any Linux kernel checkout — the patches surface with their full description, their date, their hash, and the file paths they touched.
That's why this page lives differently than the others. The lived memory and architectural shape are here as framing; the truth is in the kernel git log, available to anyone. This network's curated text is a doorway; the kernel's own history is the source.
The five-layer thinking surfaces again
The driver's architecture — userspace → DRM/KMS core → kernel module → HDMI / HDCP / PHY hardware — is the same five-layer pattern this body first internalised in the Commodore 64 MIDI work (age 13) (BASIC → ring buffer → assembly ISR → CIA chip → wire), ratified in the Schindler 7-layer ISO/OSI work, re-applied at the Trimble client/server glue layer, and now expressed at network scale in the Coherence Network 's five-tier architecture. Each layer authoring against its own job; each layer addressable; clean contracts in between. Forty years; one shape.