if (display->dpi <= 0) pr_warn("Invalid PPI, using default 420\n"); display->dpi = 420;
Samsung’s vendor tree requires exact PPI values for overlay generation. A missing or incorrect ppi parameter in BoardConfig.mk or device_samsung_*.mk . 3. Root Cause Analysis | Cause Category | Technical Explanation | |----------------|------------------------| | Build.prop corruption | ro.sf.lcd_density deleted or set to 0. Samsung devices use values like 420 (Galaxy S21), 515 (S22 Ultra), 640 (Fold inner display). | | Resolution switching bug | Samsung’s SmartProps service sometimes fails to recompute PPI after changing screen zoom or resolution. | | Hardware read failure | Display driver IC (DDIC) does not return correct physical dimensions via DisplayInfo . Common after screen replacement with non‑original part. | | Multi‑display race condition | On Z Fold series, switching between inner (7.6″) and outer (6.2″) displays can cause momentary invalid PPI for the inactive display. | | App target SDK mismatch | Apps targeting Android 12+ that don’t handle multiple display densities correctly may crash when Samsung’s WindowManager returns fallback values. | 4. Diagnostic Procedures 4.1. Check Current Display PPI on Samsung Device Method 1 – ADB:
ERROR: Invalid PPI value (0) for display 0 FATAL: DisplayMetrics density out of range Corrupted build.prop entries ( ro.sf.lcd_density ), failed display calibration, or after a system update. 2.2. Samsung Game Launcher / Game Optimizing Service (GOS) Log example: invalid ppi samsung
Camera2: Invalid PPI reported by DisplayManager - using 420 dpi default Apps that query DisplayMetrics receive xdpi or ydpi = 0.0 or negative, often due to a transient display manager state. 2.4. Custom Development (TWRP, LineageOS, Kernel Compilation) Error: error: invalid PPI value in device tree during lunch or brunch .
Invalid PPI (0,0) for display 1, skipping content scaling A third‑party launcher forced the outer display to a non‑standard DPI via wm density . When the inner display activated, its PPI was calculated relative to the outer’s modified value, resulting in zero. Root Cause Analysis | Cause Category | Technical
adb shell su mount -o rw,remount /system echo "ro.sf.lcd_density=420" >> /system/build.prop # adjust to your model reboot In /vendor/build.prop add:
persist.display.resolution.override=main:420,sub:320 (for developers) In drivers/gpu/drm/samsung/exynos_drm_display.c , ensure: | | Hardware read failure | Display driver
adb shell wm density reset Then restart both displays by switching folding mode twice.
GOS: Invalid PPI - falling back to default resolution GOS misreads display density when resolution is changed via Settings → Display → Screen resolution (HD+/FHD+/WQHD). Switching resolutions rapidly can temporarily confuse the service. 2.3. Third-Party Apps (Camera, Benchmark Tools) Log example:
adb shell wm density adb shell dumpsys display | grep -i ppi Physical density: 500 (actual PPI ~501)