Development/picky gpus

[bramoosterhuis]

Fix DRM framebuffer creation with modifiers on armv7

Problem

drmModeAddFB2WithModifiers failed on armv7 (BPI M2+, RPi 3/4) but worked on aarch64 (RPi 3/4/5). The kernel rejected framebuffers with error -22: "non-zero modifier for unused plane".

Root Cause

Code was setting modifiers for all 4 planes, but kernel requires unused planes to have modifier = 0:

modifiers.fill(buffer->Modifier());  // ❌ Sets ALL 4 planes

Fix

Initialize to zero and only set modifiers for used planes:

std::array<uint64_t, 4> modifiers = { 0, 0, 0, 0 };
modifiers[nPlanes] = bufferModifier;  // ✅ Only used planes

Changes

• DRM.cpp: Fix modifier array initialization, improve error handling/logging
• README.md: Add DRM debugging documentation (debugfs, kernel logs)
• Tests: Enhanced tracing, replaced printf with TRACE macros

Testing

✅ Tested on: RPi 3/4/5 (aarch64), BPI M2+ (armv7), RPi 3/4 (armv7)