Claude review: drm/panel: ilitek-ili9882t: Fine-tune HFP for tianma, tl121bvms07-00

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

Patch Review

**Commit Message Analysis:**

The commit message is brief but functional. It explains the problem (120.4Hz causing stylus malfunction) and the result (120Hz after fix). However, it lacks several important details:

- **Missing**: How was the refresh rate measured?
- **Missing**: Why is 120Hz the target vs 120.4Hz?
- **Missing**: Reference to panel datasheet or vendor specification
- **Missing**: Information about testing scope (which devices, which kernels)

**Technical Review:**

```c
-	.hsync_start = 1600 + 20,
-	.hsync_end = 1600 + 20 + 2,
-	.htotal = 1600 + 20 + 2 + 20,
+	.hsync_start = 1600 + 18,
+	.hsync_end = 1600 + 18 + 2,
+	.htotal = 1600 + 18 + 2 + 20,
```

**Timing Calculation Verification:**

Old timing:
- HFP (front porch): 20
- HSYNC: 2
- HBP (back porch): 20
- htotal = 1600 + 20 + 2 + 20 = 1642

New timing:
- HFP (front porch): 18
- HSYNC: 2
- HBP (back porch): 20
- htotal = 1600 + 18 + 2 + 20 = 1640

Refresh rate calculation:
- Old: 543,850,000 / (1642 × 2624) = 126.23 Hz ❌ (doesn't match stated 120.4Hz)
- New: 543,850,000 / (1640 × 2624) = 126.35 Hz ❌ (doesn't match stated 120Hz)

**CRITICAL ISSUE**: The math doesn't align with the commit message. Either:
1. The clock value is incorrect in the driver
2. The measurements in the commit message are incorrect
3. There's a pixel clock multiplier/divider not shown in this code

**Questions for Author:**

1. **Timing Source**: What is the authoritative source for these timings? Panel datasheet? Vendor recommendation? If so, please reference it.

2. **Measurement Method**: How was the refresh rate measured? Using what tool? The calculated refresh rate based on the pixel clock and totals doesn't match the stated values.

3. **Stylus Requirement**: What is the exact refresh rate tolerance required by the stylus? Is it specified in documentation?

4. **Safe Operating Range**: Does the panel datasheet specify minimum/maximum HFP values? Is 18 pixels within spec?

5. **Display Quality**: Has this been tested for:
   - Visual artifacts at the reduced HFP?
   - Proper blanking intervals?
   - Panel stability over extended operation?
   - Different temperature conditions?

6. **Regression Risk**: Was the original HFP=20 value chosen for a reason? Are there other panels using the same timings that might be affected?

**Code Quality:**

The code change itself is mechanically correct:
- Consistently updates all three related fields
- Maintains the mathematical relationship between hsync_start, hsync_end, and htotal
- Follows the existing code pattern

**Recommendation:**

**NEEDS CLARIFICATION** - The patch addresses a real issue, but the justification needs strengthening:

1. Explain the discrepancy between calculated and measured refresh rates
2. Provide datasheet reference or vendor confirmation for the new timing
3. Document the testing performed (devices, duration, scenarios)
4. Clarify if this timing is within the panel's specified operating range

The code change is minimal and low-risk, but without proper justification for the timing values, it's difficult to confirm this is the correct fix rather than just a fix that happens to work on the tested hardware.

**Minor nit**: The subject line could be more specific: "Reduce HFP from 20 to 18 pixels to correct 120Hz refresh rate" would better describe the actual change.

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Generated by Claude Code Patch Reviewer