From: Alok Tiwari alok.a.tiwari@oracle.com
[ Upstream commit bd853a59a87ecf9fc060dd54b10a3a94e9786182 ]
The MDIO read callback xgbe_phy_mii_read_c45() can propagate its return value up through phylink_mii_ioctl() to user space via netdev ioctls such as SIOCGMIIREG. Returning ENOTSUPP results in user space seeing "Unknown error", since ENOTSUPP is not a standard errno value.
Replace ENOTSUPP with EOPNOTSUPP to align with the MDIO core’s usage and ensure user space receives a proper "Operation not supported" error instead of an unknown code.
Signed-off-by: Alok Tiwari alok.a.tiwari@oracle.com Reviewed-by: Simon Horman horms@kernel.org Acked-by: Shyam Sundar S K Shyam-sundar.S-k@amd.com Link: https://patch.msgid.link/20251015025751.1532149-1-alok.a.tiwari@oracle.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
Now I have all the information I need for a complete analysis. Let me compile my findings:
## Complete Analysis
### 1. COMMIT MESSAGE ANALYSIS
**Subject:** `net: amd-xgbe: use EOPNOTSUPP instead of ENOTSUPP in xgbe_phy_mii_read_c45`
**Key points from the commit message:** - The MDIO read callback `xgbe_phy_mii_read_c45()` can propagate its return value up through `phylink_mii_ioctl()` to **user space** via netdev ioctls (SIOCGMIIREG) - Returning ENOTSUPP (error code 524) results in **user space seeing "Unknown error"** since ENOTSUPP is not a standard errno value - The fix replaces ENOTSUPP (524, kernel-internal) with EOPNOTSUPP (95, standard POSIX errno)
**Tags present:** - `Signed-off-by: Alok Tiwari alok.a.tiwari@oracle.com` - `Reviewed-by: Simon Horman horms@kernel.org` - Important! This is a well-known networking reviewer - `Acked-by: Shyam Sundar S K Shyam-sundar.S-k@amd.com` - AMD maintainer acknowledgment - `Signed-off-by: Jakub Kicinski kuba@kernel.org` - Networking maintainer
**Missing tags:** - No `Cc: stable@vger.kernel.org` - No `Fixes:` tag (though one should have been added: `Fixes: 070f6186a2f1d ("amd-xgbe: Separate C22 and C45 transactions")`)
### 2. CODE CHANGE ANALYSIS
**The diff (single line change):** ```c - ret = -ENOTSUPP; + ret = -EOPNOTSUPP; ```
**Location:** `drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c`, function `xgbe_phy_mii_read_c45()`
**Context Analysis:** The function handles MII (Media Independent Interface) Clause 45 read operations:
```c static int xgbe_phy_mii_read_c45(struct mii_bus *mii, int addr, int devad, int reg) { ... if (phy_data->conn_type == XGBE_CONN_TYPE_SFP) ret = -EOPNOTSUPP; // Already correct else if (phy_data->conn_type & XGBE_CONN_TYPE_MDIO) ret = xgbe_phy_mdio_mii_read_c45(pdata, addr, devad, reg); else ret = -ENOTSUPP; // BUG: should be -EOPNOTSUPP ```
**Root cause of the bug:** - Commit `070f6186a2f1d` ("amd-xgbe: Separate C22 and C45 transactions") introduced this function in January 2023 - Andrew Lunn correctly used `EOPNOTSUPP` for the SFP case - But **inconsistently/accidentally** used `ENOTSUPP` for the final else branch - This is clearly an oversight/typo during the refactoring
**Technical explanation of ENOTSUPP vs EOPNOTSUPP:** - `ENOTSUPP` (524): Defined in `include/linux/errno.h` as a **kernel- internal error code** originally for NFSv3 protocol - `EOPNOTSUPP` (95): Defined in `include/uapi/asm-generic/errno.h` as a **standard POSIX errno** "Operation not supported" - When kernel code returns errors through syscalls/ioctls, it must use standard POSIX errno values - User-space `strerror()` doesn't know what errno 524 means → "Unknown error 524"
### 3. CLASSIFICATION
- **Type:** Bug fix (incorrect error code returned to userspace) - **NOT a feature addition** - **NOT a device ID, quirk, or DT update** - This is fixing **incorrect API behavior** - returning a non-standard errno to userspace
### 4. SCOPE AND RISK ASSESSMENT
**Size:** - 1 line changed - 1 file touched - **Minimal scope**
**Risk:** - **EXTREMELY LOW** - This is a pure error code change - Cannot cause crashes, data corruption, or regressions - The error path itself is unchanged; only the error code returned differs - Changes from an unknown error (524) to a proper descriptive error (95)
**Similar precedents:** I found multiple similar fixes already merged: - `f82acf6fb4211` - ixgbe: use EOPNOTSUPP instead of ENOTSUPP - `21d08d1c4c29f` - igc: use EOPNOTSUPP instead of ENOTSUPP - `bc73c5885c606` - igb: use EOPNOTSUPP instead of ENOTSUPP - `ab15aabac028a` - mtd: rawnand: qcom: Use EOPNOTSUPP instead of ENOTSUPP
All these have `Fixes:` tags and address the same class of bug.
### 5. USER IMPACT
**Who is affected:** - Users of AMD XGBE network devices (10Gb Ethernet) - Any tool or application using SIOCGMIIREG/SIOCGMIIPHY ioctls - Diagnostic tools like `mii-tool`, `ethtool`, or custom MDIO access utilities
**Severity:** - When the hardware connection type is neither SFP nor MDIO, the user sees: - **Before fix:** "Unknown error 524" - confusing, hard to debug - **After fix:** "Operation not supported" - clear, standard message
**Real-world impact:** - This is a **user-visible bug** affecting error reporting - While not a crash or data corruption, it degrades user experience - Makes debugging and troubleshooting harder
### 6. STABILITY INDICATORS
- `Reviewed-by: Simon Horman` - Very experienced networking reviewer - `Acked-by: Shyam Sundar S K` - AMD driver maintainer - `Signed-off-by: Jakub Kicinski` - Net maintainer - The change is trivially correct - single character difference in error code
### 7. DEPENDENCY CHECK
**Dependencies:** None - The change is self-contained - No other commits are required - The affected code exists in all stable kernels from 6.3 onwards (where `070f6186a2f1d` was merged)
**Affected stable trees:** - 6.6.y: **Yes** - Contains the buggy commit, needs this fix - 6.10.y through 6.18.y: **Yes** - All affected - 6.1.y and earlier: **No** - The buggy code doesn't exist (function was introduced in 6.3)
### FINAL ASSESSMENT
**Pros for backporting:** 1. ✅ Fixes a **real user-visible bug** - users see "Unknown error" messages 2. ✅ **Extremely small and surgical** - single 1-line change 3. ✅ **Obviously correct** - changing from kernel-internal errno to standard POSIX errno 4. ✅ **Zero risk** - cannot introduce regressions 5. ✅ **Well reviewed** - by networking and AMD maintainers 6. ✅ **Precedent exists** - similar fixes have been applied to stable trees 7. ✅ **No dependencies** - applies cleanly to all affected stable trees
**Cons:** 1. ⚠️ No `Cc: stable@vger.kernel.org` tag - author didn't explicitly request stable backport 2. ⚠️ No `Fixes:` tag - though it clearly should have had one pointing to `070f6186a2f1d` 3. ⚠️ Minor severity - not a crash or security issue
**Conclusion:**
This commit fixes a clear bug where an incorrect kernel-internal error code (ENOTSUPP, 524) is returned to userspace instead of the proper POSIX errno (EOPNOTSUPP, 95). This causes user-space tools to display "Unknown error 524" instead of "Operation not supported", degrading user experience and making debugging harder.
The fix is: - Trivially small (1 line) - Obviously correct - Zero risk of regression - Well-reviewed by subsystem experts - Has precedent with identical fixes in other drivers
While the commit lacks explicit `Cc: stable` and `Fixes:` tags, it meets all the criteria from stable-kernel-rules.rst: it fixes "a real bug that bothers people", is small, obviously correct, and tested (reviewed by multiple maintainers).
**YES**
drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c index a56efc1bee339..35a381a83647d 100644 --- a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c +++ b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c @@ -668,7 +668,7 @@ static int xgbe_phy_mii_read_c45(struct mii_bus *mii, int addr, int devad, else if (phy_data->conn_type & XGBE_CONN_TYPE_MDIO) ret = xgbe_phy_mdio_mii_read_c45(pdata, addr, devad, reg); else - ret = -ENOTSUPP; + ret = -EOPNOTSUPP;
xgbe_phy_put_comm_ownership(pdata);