Claude review: drm/tegra: hdmi: sor: Fix error: variable ‘j’ set but not used

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Commit Metadata:**
- Author: Brahmajit Das <listout@listout.xyz>
- Upstream: 1beee8d0c263b3e239c8d6616e4f8bb700bed658
- Maintainer: Thierry Reding (NVIDIA)
- Target: Stable backport to 6.18-5.10

**Commit Message Review:**

The commit message is functional but has issues:

```
The variable j is set, however never used in or outside the loop, thus
resulting in dead code.
Building with GCC 16 results in a build error due to
-Werror=unused-but-set-variable= enabled by default.
This patch clean up the dead code and fixes the build error.
```

Issues:
- Grammar: "This patch clean up" should be "This patch cleans up"
- The message doesn't explain WHY `j` existed or whether this reveals a bug
- Contains "LLM Generated explanations" section (lines 92-195) which is highly unusual for kernel patches and should not be in the commit

**Code Review:**

**File 1: drivers/gpu/drm/tegra/hdmi.c**

Original code:
```c
size_t i, j;
...
for (i = 3, j = 0; i < size; i += 7, j += 8) {
```

Modified code:
```c
size_t i;
...
for (i = 3; i < size; i += 7) {
```

**Analysis:**
- Loop processes data in 7-byte chunks (i += 7)
- Variable `j` was incrementing by 8 (j += 8) - one byte more than the chunk size
- The comment at hdmi.c:686-692 explains the data packing format but doesn't mention why chunks are 7 bytes

**Concern:** The mismatch between incrementing by 7 (bytes) and incrementing by 8 (potentially bits * byte?) suggests `j` might have been intended for bit offset tracking but was never completed. This could indicate:
1. Dead code from refactoring
2. Incomplete implementation
3. Copy-paste error

**File 2: drivers/gpu/drm/tegra/sor.c**

Identical changes to hdmi.c:
```c
size_t i, j;
...  
for (i = 3, j = 0; i < size; i += 7, j += 8) {
```

Changed to:
```c
size_t i;
...
for (i = 3; i < size; i += 7) {
```

**Same concern applies** - the code appears to be duplicated between hdmi.c and sor.c with the same potential issue.

**Technical Issues:**

1. **Code Duplication:** The functions `tegra_hdmi_write_infopack()` and `tegra_sor_hdmi_write_infopack()` appear to have identical logic. This duplication should be refactored into a common helper function.

2. **Missing Investigation:** The patch doesn't explain:
   - When was `j` last used (if ever)?
   - Was this a regression or always dead code?
   - Does the infopack packing work correctly without this variable?

3. **Build vs Runtime:** While this fixes the build, we should verify:
   - Are HDMI infopacks being written correctly?
   - Should there be any validation that doesn't happen now?

**Positive Aspects:**

1. **Obviously Safe:** Removing truly unused variables cannot introduce runtime bugs
2. **Fixes Real Problem:** GCC 16 build breakage is legitimate
3. **Proper Signoff Chain:** Has author SoB and maintainer SoB
4. **Targeted:** Changes only what's necessary

**Questions for Maintainer:**

1. Can you verify HDMI infopack transmission works correctly on affected hardware?
2. Was `j` intended for debugging/validation that was never implemented?
3. Should these two functions be consolidated into shared code?
4. Why is there "LLM Generated explanations" in the commit message?

**Verdict:**

**Acked-by conditionally** - The code change is correct for fixing the build, but:

- The commit message should be cleaned up (remove LLM section, fix grammar)
- Investigation should be done into whether the original code was incomplete
- Consider filing a follow-up to deduplicate the hdmi.c and sor.c functions

**Risk Assessment:** Low risk for stable backport - this is purely removing dead code.

**Testing Recommendation:** Verify HDMI output on Tegra platforms (ideally Jetson boards) to ensure infopack handling remains correct.

---
Generated by Claude Code Patch Reviewer