Claude review: drm/amd/display: Wire up dcn10_dio_construct() for all pre-DCN401 generations

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Overall Series Review

Subject: drm/amd/display: Wire up dcn10_dio_construct() for all pre-DCN401 generations
Author: "Ionut Nechita (Sunlight Linux)" <sunlightlinux@gmail.com>
Patches: 3
Reviewed: 2026-03-25T07:19:08.008201

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This single patch addresses a real regression introduced by commit `b82f0759346617b2` ("drm/amd/display: Migrate DIO registers access from hwseq to dio component"), which created the `dio` abstraction but only wired it up for DCN 4.01. On all older generations, `pool->dio` remains NULL, causing the `DIO_MEM_PWR_CTRL` register write to be silently skipped. This can result in AFMT HDMI memory not being powered on during `init_hw`, leading to HDMI audio failures.

**The fix is conceptually correct** — each DCN generation needs to construct and register a `dio` object. The approach follows the existing DCN 4.01 pattern.

**However, there are several issues:**

1. **DCN21 has a serious bug** — the shift/mask structs are zero-initialized instead of being properly populated, rendering `REG_UPDATE` a no-op.
2. **Extreme code duplication** — ~30 identical lines copied across 17 files. A shared helper would be far better.
3. **The patch should be a series** — 17 modified files in a single patch is hard to review and bisect.

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