From: Muhammad Usama Anjum usama.anjum@collabora.com
[ Upstream commit cd2e7bae92bd7e65063ab8d04721d2b711ba4cbe ]
Firmware requests 2 segments at first. The first segment is of 6799360 whose allocation fails due to dma remapping not available. The success is returned to firmware. Then firmware asks for 22 smaller segments instead of 2 big ones. Those get allocated successfully. At suspend/ hibernation time, these segments aren't freed as they will be reused by firmware after resuming.
After resuming, the firmware asks for the 2 segments again with the first segment of 6799360 size. Since chunk->vaddr is not NULL, the type and size are compared with the previous type and size to know if it can be reused or not. Unfortunately, it is detected that it cannot be reused and this first smaller segment is freed. Then we continue to allocate 6799360 size memory which fails and ath11k_qmi_free_target_mem_chunk() is called which frees the second smaller segment as well. Later success is returned to firmware which asks for 22 smaller segments again. But as we had freed 2 segments already, we'll allocate the first 2 new smaller segments again and reuse the remaining 20. Hence 20 small segments are being reused instead of 22.
Add skip logic when vaddr is set, but size/type don't match. Use the same skip and success logic as used when dma_alloc_coherent() fails. By skipping, the possibility of resume failure due to kernel failing to allocate memory for QMI can be avoided.
kernel: ath11k_pci 0000:03:00.0: failed to allocate dma memory for qmi (524288 B type 1) ath11k_pci 0000:03:00.0: failed to allocate qmi target memory: -22
Tested-on: WCN6855 WLAN.HSP.1.1-03926.13-QCAHSPSWPL_V2_SILICONZ_CE-2.52297.6
Signed-off-by: Muhammad Usama Anjum usama.anjum@collabora.com Reviewed-by: Baochen Qiang quic_bqiang@quicinc.com Link: https://patch.msgid.link/20250428080242.466901-1-usama.anjum@collabora.com Signed-off-by: Jeff Johnson jeff.johnson@oss.qualcomm.com Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis of this commit and the Linux kernel ath11k QMI code, here's my assessment: **YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Critical Bug Fix for Resume/Hibernation Failures ### Problem Description The commit fixes a critical logic flaw in QMI memory reuse during firmware reload scenarios, particularly affecting suspend/resume and hibernation cycles. The bug causes resume failures with errors like: ``` kernel: ath11k_pci 0000:03:00.0: failed to allocate dma memory for qmi (524288 B type 1) ath11k_pci 0000:03:00.0: failed to allocate qmi target memory: -22 ``` ### Code Analysis of the Fix **The core issue (lines 1996-2003 in the diff):** ```c + if (ab->qmi.mem_seg_count <= ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT) { + ath11k_dbg(ab, ATH11K_DBG_QMI, + "size/type mismatch (current %d %u) (prev %d %u), try later with small size\n", + chunk->size, chunk->type, + chunk->prev_size, chunk->prev_type); + ab->qmi.target_mem_delayed = true; + return 0; + } ``` **Before the fix:** When firmware requests different memory segment sizes/types than previously allocated (common during resume), the driver would: 1. Free the existing memory chunks with `dma_free_coherent()` 2. Try to allocate the new larger size (often 6+ MB) 3. Fail due to memory fragmentation after hibernation 4. Free remaining chunks, causing loss of successfully allocated smaller segments **After the fix:** When size/type mismatch occurs and segment count ≤ 5 (`ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT`), the driver: 1. Sets `target_mem_delayed = true` 2. Returns success immediately (skipping allocation) 3. Allows firmware to fall back to requesting smaller chunks 4. Preserves existing memory allocations for reuse ### Why This Qualifies for Stable Backporting 1. **Fixes Important User-Affecting Bug**: Resume/hibernation failures directly impact user experience and system reliability 2. **Minimal and Contained Change**: The fix adds only 8 lines of code with a simple conditional check using existing mechanisms (`target_mem_delayed` flag and `ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT` constant) 3. **Low Regression Risk**: - Uses existing, well-tested delayed allocation mechanism - Only affects the specific error path for size/type mismatches - Maintains backward compatibility with all existing behavior 4. **Critical Subsystem**: WiFi connectivity is essential functionality, and resume failures can render systems unusable 5. **Clear Root Cause**: The commit message and code changes clearly identify and fix a specific logic error in memory management 6. **Follows Stable Rules**: - Important bugfix (resume failures) - Small and self-contained - No architectural changes - Confined to ath11k subsystem ### Validation Against Similar Commits Looking at the historical examples: - **Similar Commit #1 (YES)**: Also fixes QMI memory allocation warnings/failures, uses similar logic with `prev_size` fields - **Similar Commit #4 (YES)**: Implements the `target_mem_delayed` mechanism this fix builds upon This commit follows the same pattern as previously backported QMI memory fixes, addressing a critical failure scenario with minimal risk. ### Technical Validation The fix leverages the existing delayed allocation negotiation mechanism between driver and firmware, which has been proven stable since its introduction. By using `target_mem_delayed = true`, it allows firmware to adaptively request smaller, more allocation-friendly memory segments rather than failing outright. The `ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT = 5` threshold ensures this optimization only applies to initial firmware memory requests (≤5 segments), not to scenarios where firmware has already adapted to smaller chunks (>5 segments). **Conclusion**: This is a well-contained, low-risk fix for a critical user-facing issue that should definitely be backported to stable kernels.
drivers/net/wireless/ath/ath11k/qmi.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/drivers/net/wireless/ath/ath11k/qmi.c b/drivers/net/wireless/ath/ath11k/qmi.c index 4f8b08ed1bbc6..83a48a77c53ee 100644 --- a/drivers/net/wireless/ath/ath11k/qmi.c +++ b/drivers/net/wireless/ath/ath11k/qmi.c @@ -1993,6 +1993,15 @@ static int ath11k_qmi_alloc_target_mem_chunk(struct ath11k_base *ab) chunk->prev_size == chunk->size) continue;
+ if (ab->qmi.mem_seg_count <= ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT) { + ath11k_dbg(ab, ATH11K_DBG_QMI, + "size/type mismatch (current %d %u) (prev %d %u), try later with small size\n", + chunk->size, chunk->type, + chunk->prev_size, chunk->prev_type); + ab->qmi.target_mem_delayed = true; + return 0; + } + /* cannot reuse the existing chunk */ dma_free_coherent(ab->dev, chunk->prev_size, chunk->vaddr, chunk->paddr);