Claude review: drm: shmobile: Fix white screen after resume when LCDC is stopped

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Overall Series Review

Subject: drm: shmobile: Fix white screen after resume when LCDC is stopped
Author: phucduc.bui@gmail.com
Patches: 1
Reviewed: 2026-03-22T04:28:52.005399

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This is a single, well-motivated bugfix patch for the shmobile LCDC driver. The problem is clearly described: after suspend/resume, both register sets (A and B) are reset to 0, but the original code only wrote to the mirror (Set B) and relied on a Frame End interrupt to trigger the hardware register switching. When the controller is stopped (DO=0), no Frame End interrupt occurs, so Set A stays at 0 and the display shows white.

The fix is correct and minimal. It checks whether the display output is active (LDCNT2R_DO) and uses the appropriate write path:
- **DO=1 (running):** Use `lcdc_write_mirror()` + toggle `LDRCNTR_MRS` as before (the normal double-buffered update path).
- **DO=0 (stopped):** Use `lcdc_write()` which writes to both Set A and Set B directly, ensuring valid addresses are present when output is re-enabled.

The patch has Tested-by and Reviewed-by from the subsystem maintainer (Geert Uytterhoeven). It looks ready to merge.

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