fsi: master-ast-cf: fix relative address arithmetic

[staticpayload]

Summary

• fix relative-address subtraction to avoid implementation-defined unsigned wrap
• keep behavior identical for in-range offsets

Testing

• AWS EC2 (eu-central-2), Amazon Linux 2023 via SSM
• make defconfig
• scripts/config --enable FSI --enable FSI_MASTER_AST_CF
• make W=1 drivers/fsi/fsi-master-ast-cf.o

Log: /Users/staticpayload/kernel-upstream/agent_notes/aws-build-fsi-ast-cf.json

Summary by CodeRabbit

• Bug Fixes
  • Corrected unaligned read and write length calculations in FSI operations to ensure proper alignment and boundary handling.
  • Fixed relative address calculation to properly support signed address ranges and improve validation.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Two FSI driver files received bug fix updates: fsi-core.c modified per-iteration read/write length calculations to properly account for unaligned offsets and remaining byte counts, while fsi-master-ast-cf.c changed address calculation to use signed arithmetic for correct negative offset validation.

Changes

Cohort / File(s)	Summary
FSI Core Length Calculation Fix drivers/fsi/fsi-core.c	Updated cfam_read and cfam_write per-iteration length calculations from min(count, 4) - (off & 0x3) to min(4 - (off & 0x3), count - total_len) to correctly bound chunk sizes by both alignment remainder and remaining byte count.
FSI Master Address Calculation Fix drivers/fsi/fsi-master-ast-cf.c	Changed rel_addr calculation to cast operands to int32_t before subtraction, enabling signed arithmetic for proper validation against the -256..255 range.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A leap of logic, bounds now tight,
Signed offsets hop just right,
Min and max in perfect dance,
Alignment fixes at a glance! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fsi: master-ast-cf: fix relative address arithmetic' directly matches the main change in the PR, which fixes signed arithmetic for relative address calculations in the fsi-master-ast-cf driver.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

Warning

Review ran into problems

🔥 Problems

Git: Failed to clone repository. Please run the @coderabbitai full review command to re-trigger a full review. If the issue persists, set path_filters to include or exclude specific files.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}