From: Rand Deeb rand.sec96@gmail.com
[ Upstream commit cdcb3804eeda24d588348bbab6766cf14fddbeaa ]
The current implementation of `ixgbe_write_i2c_combined_generic_int` and `ixgbe_write_i2c_byte_generic_int` sets `max_retry` to `1`, which makes the condition `retry < max_retry` always evaluate to `false`. This renders the retry mechanism ineffective, as the debug message and retry logic are never executed.
This patch increases `max_retry` to `3` in both functions, aligning them with the retry logic in `ixgbe_read_i2c_combined_generic_int`. This ensures that the retry mechanism functions as intended, improving robustness in case of I2C write failures.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Rand Deeb rand.sec96@gmail.com Tested-by: Rinitha S sx.rinitha@intel.com (A Contingent worker at Intel) Signed-off-by: Tony Nguyen anthony.l.nguyen@intel.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Bug Analysis **Critical Logic Flaw:** The commit fixes a fundamental bug where the retry logic in I2C write functions was completely ineffective. With `max_retry = 1`, the condition `retry < max_retry` would only allow `retry = 0`, meaning the retry loop would never execute more than once, making the entire retry mechanism useless. **Code Impact:** The change from `max_retry = 1` to `max_retry = 3` in both: - `ixgbe_write_i2c_combined_generic_int()` (line ~170) - `ixgbe_write_i2c_byte_generic_int()` (line ~2288) This aligns with the existing `ixgbe_read_i2c_combined_generic_int()` function which already uses `max_retry = 3`. ## Backport Suitability Criteria **1. Fixes Important User-Affecting Bug:** ✓ - I2C write failures directly impact SFP/QSFP module detection and configuration - Affects `ethtool --identify` LED functionality - Can cause intermittent network interface initialization failures - Users would experience unreliable hardware detection and configuration **2. Small and Contained Change:** ✓ - Only changes two integer values from 1 to 3 - No architectural changes or new functionality - Minimal risk of introducing regressions - Affects only the specific I2C write retry mechanism **3. No Side Effects Beyond the Fix:** ✓ - Simply enables existing retry logic to work as intended - Doesn't change the fundamental I2C communication protocol - Maintains consistency with read operations - No new code paths introduced **4. Critical Subsystem Impact:** ✓ - Network driver functionality is critical for system operation - I2C communication is essential for modern network hardware management - Affects Intel ixgbe NICs which are widely deployed in enterprise environments **5. Clear Bug Evidence:** ✓ - Linux Verification Center found this with static analysis (SVACE) - Logic flaw is mathematically provable (retry < 1 never allows retry) - Consistent with similar commits in the pattern (Similar Commit #1 shows retry count adjustments are appropriate for backporting) ## Comparison to Historical Patterns This commit closely matches **Similar Commit #1** (Backport Status: YES) which also modified I2C retry counts in ixgbe. That commit reduced retry counts to avoid regressions, while this one increases retry counts to fix broken logic - both are stability improvements worthy of backporting. Unlike **Similar Commit #2** (Backport Status: NO) which was architectural refactoring, this commit fixes a clear functional defect without introducing new features or code reorganization. ## Risk Assessment **Low Risk:** - Increasing retries from effectively 0 to 3 cannot make things worse - The retry mechanism already existed and was intended to be used - 3 retries aligns with established patterns in the same driver - Intel has tested this change (as indicated by the "Tested- by" tag) **High Impact:** - Fixes complete failure of I2C write retry mechanism - Improves reliability of critical network hardware functionality - Addresses systematic logic flaw affecting all ixgbe deployments This commit represents exactly the type of important, low- risk bug fix that stable trees are designed to receive.
drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c index 0a03a8bb5f886..2d54828bdfbbc 100644 --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c @@ -167,7 +167,7 @@ int ixgbe_write_i2c_combined_generic_int(struct ixgbe_hw *hw, u8 addr, u16 reg, u16 val, bool lock) { u32 swfw_mask = hw->phy.phy_semaphore_mask; - int max_retry = 1; + int max_retry = 3; int retry = 0; u8 reg_high; u8 csum; @@ -2285,7 +2285,7 @@ static int ixgbe_write_i2c_byte_generic_int(struct ixgbe_hw *hw, u8 byte_offset, u8 dev_addr, u8 data, bool lock) { u32 swfw_mask = hw->phy.phy_semaphore_mask; - u32 max_retry = 1; + u32 max_retry = 3; u32 retry = 0; int status;