From: Cristian Marussi cristian.marussi@arm.com
[ Upstream commit 092b9e2ce6dd63d2f36822751a51957412706986 ]
Avoid attempting to initialize RAW mode when the debug subsystem itself has failed to initialize, since doing so is pointless and emits misleading error messages.
Signed-off-by: Cristian Marussi cristian.marussi@arm.com Message-Id: 20251014115346.2391418-3-cristian.marussi@arm.com Signed-off-by: Sudeep Holla sudeep.holla@arm.com Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
Now I have enough information to make my determination. Let me create a comprehensive analysis:
## BACKPORT ANALYSIS DECISION
**Backport Status: YES**
---
## COMPREHENSIVE ANALYSIS
### 1. CODE CHANGE ANALYSIS
The commit makes two related changes:
**Change 1** (drivers/firmware/arm_scmi/driver.c:3047-3048): ```c - if (!info->dbg) - return -EINVAL; ``` Removes the NULL check from inside `scmi_debugfs_raw_mode_setup()`.
**Change 2** (drivers/firmware/arm_scmi/driver.c:3221): ```c - if (IS_ENABLED(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT)) { + if (info->dbg && IS_ENABLED(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT)) { ``` Adds guard condition to prevent calling the function when `info->dbg` is NULL.
### 2. SEMANTIC ANALYSIS PERFORMED
**Tools Used:** - `git log` and `git show` for commit history analysis - `Grep` for code pattern searches across SCMI subsystem - `Read` for examining driver code and Kconfig - Task agent (Explore) for understanding SCMI ecosystem context - Git blame and tag analysis for version tracking
**Key Findings from Analysis:**
**Impact Scope (from code examination):** - Function `scmi_debugfs_raw_mode_setup()` is called from only ONE location: `scmi_probe()` at line 3222 - Function accesses `info->dbg->top_dentry` at line 3068, which would be a **NULL pointer dereference** if the removed check wasn't there - The calling site now has proper guard, so function is never called with NULL dbg
**Caller Analysis:** - `scmi_probe()` is the driver probe function - called during device initialization - Prior commits in series (2290ab43b9d8e, 289ce7e9a5e1a) fixed NULL handling in debug helpers - This commit completes the debug failure handling by preventing pointless RAW init attempt
**Dependency Analysis:** - RAW mode requires debugfs (CONFIG dependency in Kconfig line 35) - `scmi_raw_mode_init()` expects valid `top_dentry` parameter (line 3068) - If debug setup fails, `info->dbg` is NULL, making RAW mode init impossible
### 3. BUG IMPACT ANALYSIS
**Affected Kernel Versions:** - Introduced: v6.3-rc1 (commit 7063887b53860, January 2023) - Fixed: v6.18-rc3 (commit 092b9e2ce6dd6, October 2025) - **Affected range: v6.3 through v6.17**
**Failure Scenario:** ```c // Before fix - in scmi_probe(): if (scmi_top_dentry) { info->dbg = scmi_debugfs_common_setup(info); // Returns NULL on failure if (!info->dbg) dev_warn(dev, "Failed to setup SCMI debugfs.\n");
if (IS_ENABLED(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT)) { ret = scmi_debugfs_raw_mode_setup(info); // Called with NULL dbg! if (!coex) { // Default config if (ret) // ret = -EINVAL goto clear_dev_req_notifier; // PROBE FAILS! return 0; } } } ```
**Real-World Impact:** - **Who is affected**: Development/testing systems with CONFIG_ARM_SCMI_RAW_MODE_SUPPORT=y - **When it triggers**: When debugfs initialization fails (no debugfs support, memory failure, mount issues) - **What breaks**: **Entire SCMI driver probe fails** → system may not boot - **Criticality**: SCMI manages power domains, clocks, DVFS, thermal sensors - critical for ARM platforms
From Explore agent findings: - SCMI is used on STM32MP, ARM Juno, NXP i.MX95 platforms - Controls essential services: CPU frequency, power states, system shutdown/reboot - Kconfig notes it "may be needed early in boot" for power control
**Severity Assessment:** - **Medium-High for affected configurations** - Not production issue (RAW mode is debug/testing feature per Kconfig line 42) - But complete driver failure is **unacceptable** for development systems - Misleading error messages make debugging difficult
### 4. ARCHITECTURAL & SIDE EFFECTS
**Architectural Impact:** None - No data structure changes - No API modifications - No changes to core SCMI protocol handling
**Side Effects:** Positive only - Prevents probe failure when debugfs fails - Eliminates misleading error messages - Improves graceful degradation - No functional changes to success path
### 5. STABLE TREE COMPLIANCE
**Compliance Check:** ✅ **Bug fix**: Yes - fixes probe failure ✅ **Small and contained**: 2 simple changes in 1 file ✅ **Obviously correct**: Guard check before function call ✅ **No new features**: Pure bug fix ✅ **No architectural changes**: Minimal scope ✅ **Low regression risk**: Only affects error path
**Stable Tree Rules Alignment:** - Fixes important bug (probe failure) - Self-contained change - Easy to review and verify - Part of coordinated fix series (related commits already backported)
### 6. BACKPORT INDICATORS
**Evidence for backporting:** - **Related commits already backported**: Commit 2290ab43b9d8e (with Fixes tag) has been backported to multiple stable trees (7056e61a28a83, 4c0f9a50f2e98, fae8405cfddb0, 58d3e2680bea9, 30c89140a4ddc, 75446183128d2) - **Part of fix series**: This is patch 3/3 in a coordinated series addressing debug initialization failures - **Fixes merged in mainline**: Present in v6.18-rc3, merged via arm/fixes tree (71a5970259c3f) - **No Cc: stable tag**: But related patches were backported, suggesting subsystem maintainers want the series in stable
**Evidence against backporting:** - No explicit "Fixes:" tag (but commit message clearly states it fixes a problem) - No "Cc: stable@vger.kernel.org" tag - Only affects debug/testing configuration
### 7. DEPENDENCY CHECK
**Depends on:** - None - independent fix - Works better with commits 2290ab43b9d8e and 289ce7e9a5e1a (already backported)
**Required by:** - None identified
---
## FINAL RECOMMENDATION
**YES - This commit SHOULD be backported to stable kernel trees.**
**Justification:**
1. **Fixes probe failure**: When debugfs fails + RAW mode enabled (without coex), entire SCMI driver fails to load, breaking critical platform services
2. **Completes backported series**: Related fixes (2290ab43b9d8e, 289ce7e9a5e1a) already backported to stable. This commit completes the debug failure handling
3. **Low risk, high correctness**: Minimal change, obviously correct logic (guard before function call)
4. **Stable tree compliant**: Small, contained, bug-fix-only change with no architectural impact
5. **Affects supported feature**: CONFIG_ARM_SCMI_RAW_MODE_SUPPORT exists in stable kernels since v6.3
6. **Graceful degradation**: Enables proper fallback behavior when debug subsystem fails
**Target stable trees:** v6.3+ (where RAW mode was introduced)
**Priority:** Medium - affects development/testing systems, not production, but fixes complete driver failure
drivers/firmware/arm_scmi/driver.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c index bd56a877fdfc8..85392228d1739 100644 --- a/drivers/firmware/arm_scmi/driver.c +++ b/drivers/firmware/arm_scmi/driver.c @@ -3044,9 +3044,6 @@ static int scmi_debugfs_raw_mode_setup(struct scmi_info *info) u8 channels[SCMI_MAX_CHANNELS] = {}; DECLARE_BITMAP(protos, SCMI_MAX_CHANNELS) = {};
- if (!info->dbg) - return -EINVAL; - /* Enumerate all channels to collect their ids */ idr_for_each_entry(&info->tx_idr, cinfo, id) { /* @@ -3218,7 +3215,7 @@ static int scmi_probe(struct platform_device *pdev) if (!info->dbg) dev_warn(dev, "Failed to setup SCMI debugfs.\n");
- if (IS_ENABLED(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT)) { + if (info->dbg && IS_ENABLED(CONFIG_ARM_SCMI_RAW_MODE_SUPPORT)) { ret = scmi_debugfs_raw_mode_setup(info); if (!coex) { if (ret)