[PATCH AUTOSEL 7.0-6.12] bus: mhi: host: pci_generic: Add Telit FE912C04 modem support

[Sasha Levin <sashal@kernel.org>]

From: Daniele Palmas <dnlplm@gmail.com>

[ Upstream commit ac12b852b4ead4a586299c8f68cdcbcaf1bf6cbc ]

Add SDX35 based modem Telit FE912C04, reusing FN920C04 configuration.

01:00.0 Unassigned class [ff00]: Qualcomm Device 011a
        Subsystem: Device 1c5d:2045

Signed-off-by: Daniele Palmas <dnlplm@gmail.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Link: https://patch.msgid.link/20260323122837.3406521-1-dnlplm@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my analysis, this is a clear device-ID addition to an existing
driver. Let me provide the comprehensive analysis.

## Phase 1: Commit Message Forensics

**Step 1.1 - Subject line parse:**
Record: subsystem=`bus: mhi: host: pci_generic`, action verb=`Add`,
summary=`Add Telit FE912C04 modem support`

**Step 1.2 - Tag analysis:**
- Signed-off-by: Daniele Palmas (author, repeat contributor for Telit
  modems)
- Signed-off-by: Manivannan Sadhasivam (MHI maintainer)
- Link: lore.kernel.org thread
  (`20260323122837.3406521-1-dnlplm@gmail.com`)
- No Fixes:, no Cc: stable, no Reported-by:, no Tested-by:, no Reviewed-
  by:, no syzbot

Record: Standard maintainer-applied patch with no fix-related tags.

**Step 1.3 - Commit body:**
Single-paragraph body: states the device is SDX35-based, will reuse the
existing FN920C04 configuration, and includes an `lspci` snippet
confirming the PCI subsystem ID `1c5d:2045`. No bug description, no
symptom, no crash trace.

Record: This is a hardware enablement commit, not a bug fix.

**Step 1.4 - Hidden bug fix detection:**
The verb is "Add" with "modem support". No "handle", "ensure",
"prevent", "fix", "clean up". The diff is a textbook device-ID addition
reusing existing config. Not a hidden bug fix.

Record: Pure hardware enablement - new PCI device ID + descriptor for an
existing driver.

## Phase 2: Diff Analysis

**Step 2.1 - Inventory:**
- Files: `drivers/bus/mhi/host/pci_generic.c` only
- Total: +13 lines, -0 lines
- Functions modified: none (only adds a static struct and a table entry)
- Scope: single-file, surgical, additive

**Step 2.2 - Code flow change:**
- Before: `mhi_pci_id_table[]` did not match PCI VID 0x17cb / SVID
  `1c5d:2045`
- After: PCI core probes → matches new entry → loads MHI driver with
  `mhi_telit_fe912c04_info` (which uses already-existing
  `modem_telit_fn920c04_config`)

Record: Adds one new PCI table row + one descriptor struct. No
behavioral change for any existing device.

**Step 2.3 - Bug mechanism:**
Not a bug fix. This is category (h) "Hardware workarounds → Device ID
additions" from the stable rules exceptions.

**Step 2.4 - Fix quality:**
- Obviously correct: a new struct with same fields as
  `mhi_telit_fe990b40_info`, reusing `modem_telit_fn920c04_config`
  already proven for SDX35 hardware
- Minimal/surgical: 13 lines, contained in tables only
- Regression risk: nil for any user without that exact 1c5d:2045 device;
  for users with it, there is no other code path (driver simply wouldn't
  bind today)

## Phase 3: Git History Investigation

**Step 3.1 - git blame:** Not applicable - no existing buggy code is
being fixed; only additions.

**Step 3.2 - Fixes: tag:** Not present (and not expected for a device-ID
addition).

**Step 3.3 - File history (recent same-file commits):**
```
ac12b852b4ead Add Telit FE912C04 modem support       <- this commit
6eaee77923ddf Add Telit FE990B40 modem support
00559ba3ae740 Add Telit FN990B40 modem support
6348f62ef7ecc Add Telit FN920C04 modem support
```
Record: This is the latest in a steady cadence of Telit modem device-ID
additions. All prior siblings in this series were backported to stable
(verified below).

**Step 3.4 - Author history:**
Daniele Palmas is a long-time Telit modem submitter; Manivannan
Sadhasivam is the MHI subsystem maintainer who applied it.

**Step 3.5 - Dependencies:**
- Requires `modem_telit_fn920c04_config` (introduced by 6348f62ef7ecc,
  backported to 6.12+).
- Diff context anchored on `mhi_telit_fe990b40_info` (introduced by
  6eaee77923ddf, backported to 6.12+).
Both dependencies exist in stable 6.12.y, 6.18.y, 6.19.y, 7.0.y.

## Phase 4: Mailing List Investigation

**Step 4.1 - b4 dig:**
- `b4 dig -c ac12b852b4ead4a586299c8f68cdcbcaf1bf6cbc` matched by patch-
  id and resolved to
  https://lore.kernel.org/all/20260323122837.3406521-1-dnlplm@gmail.com/
- Single revision (PATCH 1/1), no v2/v3.
- Maintainer reply: "Applied, thanks!" - no review concerns, no NAKs, no
  stable nomination requested.

**Step 4.2 - Reviewers:** Patch sent to maintainer Manivannan
Sadhasivam, mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org. Right
people CC'd. Maintainer applied.

**Step 4.3 - Bug reports:** Not applicable; no Reported-by/Link to bug
tracker.

**Step 4.4 - Series context:** Standalone single-patch.

**Step 4.5 - Stable list:** No prior stable discussion (typical for a
new device ID).

## Phase 5: Code Semantic Analysis

**Step 5.1 - Functions:** None modified; only data-structure additions.

**Step 5.2-5.4 - Reachability:** The new entry is reachable only when
the PCI core enumerates a device with VID=QCOM(0x17cb), DID=0x011a,
SVID=0x1c5d, SSID=0x2045. No other code path is affected.

**Step 5.5 - Similar patterns:** The same pattern (adding
`mhi_pci_dev_info` + `pci_device_id`) is used for FN920C04, FN990B40,
FE990B40 - all backported.

## Phase 6: Cross-Referencing & Stable Tree Analysis

**Step 6.1 - Buggy code in stable:** N/A (no bug being fixed).

**Step 6.2 - Backport feasibility:**
- 7.0.y, 6.19.y, 6.18.y, 6.12.y: dependencies present → patch should
  apply cleanly with at most trivial offset.
- 6.6.y: `modem_telit_fn920c04_config` and `mhi_telit_fe990b40_info` are
  NOT in `pci_generic.c` → patch will not apply cleanly. Backport for
  6.6.y would require backporting prerequisites first (which were not
  selected for 6.6.y).

**Step 6.3 - Related fixes already in stable:**
- 6348f62ef7ecc (FN920C04) → backported as 4e3297ec0c469
- 00559ba3ae740 (FN990B40) → backported as 1ee92e44c3316 / 7bce22989c7b7
- 6eaee77923ddf (FE990B40) → backported as 9bef8beef1557 / 3a15c519d2b0f

The pattern clearly establishes that every prior Telit/MHI device-ID
addition in this file has been backported.

## Phase 7: Subsystem Context

Subsystem: `drivers/bus/mhi/host/` - host-side MHI bus controllers,
primarily for Qualcomm SoC modems used as PCIe-attached cellular cards.
Criticality: PERIPHERAL (hardware-specific) but with real-world users
(laptops, IoT, M2M deployments).
Activity: Active and well-maintained.

## Phase 8: Impact and Risk

**Step 8.1 - Affected users:** Owners of Telit FE912C04 modems (a real
product). Without this patch the device will not bind to any kernel
driver.

**Step 8.2 - Trigger:** Plugging in the specific hardware. No security
relevance, no unprivileged trigger.

**Step 8.3 - Failure mode without patch:** Device simply doesn't work
(no driver binds). With patch: device works using existing, tested
FN920C04 channel/event configuration.

**Step 8.4 - Risk-benefit:**
- Benefit: enables hardware on stable users' systems - high for affected
  users, none for others
- Risk: ~0 - additive only, scoped to one specific PCI subsystem ID,
  reuses already-validated config

## Phase 9: Final Synthesis

**Stable rules checklist:**
1. Obviously correct? YES - reuses already-validated
   `modem_telit_fn920c04_config`
2. Fixes a real bug? Strictly no, but enables real hardware (explicit
   stable exception)
3. Important issue? Hardware enablement, qualifies under exception
4. Small and contained? YES - 13 lines, single file
5. No new features/APIs? YES - no userspace API change, no new module
   behavior
6. Applies to stable? YES for 6.12.y, 6.18.y, 6.19.y, 7.0.y; NO for
   6.6.y (needs prerequisites)

**Exception category:** "NEW DEVICE IDs" - explicitly listed as an
allowed addition for stable.

**Precedent:** All three sibling Telit MHI device-ID additions
(FN920C04, FN990B40, FE990B40) have been backported to stable,
establishing clear policy for this exact scenario.

## Verification

- [Phase 1] Read commit message: confirmed only Signed-off-by (author +
  maintainer) and Link tags; no Fixes/Reported-by/Cc:stable/Tested-
  by/Reviewed-by.
- [Phase 2] `git show ac12b852b4ead`: confirmed +13/-0 lines, all in
  `drivers/bus/mhi/host/pci_generic.c`; verified one new
  `mhi_pci_dev_info` struct and one `pci_device_id` table entry.
- [Phase 3.3] `git log --oneline -- drivers/bus/mhi/host/pci_generic.c`:
  confirmed prior commits FN920C04, FN990B40, FE990B40.
- [Phase 3.5] `grep modem_telit_fn920c04_config pci_generic.c`:
  confirmed config struct exists at line 846 in current tree (introduced
  by FN920C04 commit).
- [Phase 4.1] `b4 dig -c ac12b852b4ead`: matched single-revision thread
  at lore.kernel.org/all/20260323122837.3406521-1-dnlplm@gmail.com/;
  saved mbox; read maintainer's "Applied, thanks!" reply with no
  concerns.
- [Phase 6.2] `git cat-file -p stable/linux-
  {6.12,6.18,6.19,7.0}.y:drivers/bus/mhi/host/pci_generic.c`: confirmed
  `modem_telit_fn920c04_config` and `mhi_telit_fe990b40_info` (anchor
  lines for the diff) are present in 6.12.y, 6.18.y, 6.19.y, 7.0.y
  stable trees.
- [Phase 6.2] `git cat-file -p
  stable/linux-6.6.y:drivers/bus/mhi/host/pci_generic.c`: confirmed
  `modem_telit_fn920c04_config` is NOT in 6.6.y (only earlier modem
  configs present); 6.6.y would need prerequisites.
- [Phase 6.3] `git show 4e3297ec0c469 / 1ee92e44c3316 / 9bef8beef1557`:
  confirmed these are stable backports of upstream commits
  6348f62ef7ecc, 00559ba3ae740, 6eaee77923ddf with "[upstream] commit
  ... upstream." in the body, signed by Greg KH.
- [Phase 8] Diff inspection: no new module parameter, no sysfs, no
  userspace ABI; only additions to two static tables.
- UNVERIFIED: Could not verify without trying that the patch will apply
  with zero context conflict on stable 6.12.y - but anchor-line
  `mhi_telit_fe990b40_info` is present, so a clean apply is highly
  likely.

The change is a textbook PCI device-ID addition for an existing driver,
reusing already-validated configuration, with strong precedent that all
three sibling device-ID additions in the same file have been accepted to
stable. Risk is essentially nil; the benefit is enabling real hardware
for stable users. It falls squarely under the explicitly documented "NEW
DEVICE IDs" exception.

**YES**

 drivers/bus/mhi/host/pci_generic.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/bus/mhi/host/pci_generic.c b/drivers/bus/mhi/host/pci_generic.c
index 425362037830e..5db3df20088fd 100644
--- a/drivers/bus/mhi/host/pci_generic.c
+++ b/drivers/bus/mhi/host/pci_generic.c
@@ -892,6 +892,16 @@ static const struct mhi_pci_dev_info mhi_telit_fe990b40_info = {
 	.edl_trigger = true,
 };
 
+static const struct mhi_pci_dev_info mhi_telit_fe912c04_info = {
+	.name = "telit-fe912c04",
+	.config = &modem_telit_fn920c04_config,
+	.bar_num = MHI_PCI_DEFAULT_BAR_NUM,
+	.dma_data_width = 32,
+	.sideband_wake = false,
+	.mru_default = 32768,
+	.edl_trigger = true,
+};
+
 static const struct mhi_pci_dev_info mhi_netprisma_lcur57_info = {
 	.name = "netprisma-lcur57",
 	.edl = "qcom/prog_firehose_sdx24.mbn",
@@ -919,6 +929,9 @@ static const struct pci_device_id mhi_pci_id_table[] = {
 	/* Telit FN920C04 (sdx35) */
 	{PCI_DEVICE_SUB(PCI_VENDOR_ID_QCOM, 0x011a, 0x1c5d, 0x2020),
 		.driver_data = (kernel_ulong_t) &mhi_telit_fn920c04_info },
+	/* Telit FE912C04 (sdx35) */
+	{ PCI_DEVICE_SUB(PCI_VENDOR_ID_QCOM, 0x011a, 0x1c5d, 0x2045),
+		.driver_data = (kernel_ulong_t) &mhi_telit_fe912c04_info },
 	{ PCI_DEVICE(PCI_VENDOR_ID_QCOM, 0x011a),
 		.driver_data = (kernel_ulong_t) &mhi_qcom_sdx35_info },
 	{ PCI_DEVICE(PCI_VENDOR_ID_QCOM, 0x0304),
-- 
2.53.0