[PATCH AUTOSEL 6.16 74/85] usb: dwc3: xilinx: add shutdown callback

[Sasha Levin <sashal@kernel.org>]

From: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>

[ Upstream commit 70627bf82e36e61c40c3315e1206e4ea4c02e668 ]

Adds a shutdown callback to ensure that the XHCI stack is properly
shutdown in reboot/shutdown path.

In kexec flow, kernel_restart_prepare() performs actions necessary
to prepare the system for a restart and invokes device_shutdown. To
ensure proper shutdown attach the dwc3 shutdown implementation which
mirrors the remove method.

$ kexec -e

<snip>
xhci-hcd xhci-hcd.0.auto: remove, state 1
usb usb1: USB disconnect, device number 1
usb 1-1: USB disconnect, device number 6
xhci-hcd xhci-hcd.0.auto: USB bus 1 deregistered
kexec_core: Starting new kernel

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Link: https://lore.kernel.org/r/1748977771-714153-1-git-send-email-radhey.shyam.pandey@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

**Backport Status: YES**

This commit should be backported to stable kernel trees. Here's my
detailed analysis:

## Analysis of the Commit

### 1. **Bug Fix Nature**
This commit fixes a real bug where the USB XHCI stack is not properly
shut down during kexec operations. The commit message explicitly shows
the issue - when `kexec -e` is executed, the XHCI controller is removed
but without a proper shutdown sequence, which can lead to:
- Memory corruption if the controller continues DMA operations
- System instability during kexec transitions
- Potential crashes after kexec

### 2. **Simple and Contained Fix**
The code change is minimal and low-risk:
```diff
+       .shutdown       = dwc3_xlnx_remove,
```
It simply reuses the existing `dwc3_xlnx_remove` function as the
shutdown callback. This is a common pattern in kernel drivers.

### 3. **Follows Established Pattern**
My analysis shows this follows an established pattern in the dwc3 driver
family:
- `dwc3-of-simple.c` uses its remove function for shutdown
- `dwc3-rtk.c` has a dedicated shutdown function that calls similar
  cleanup
- The recent Tegra XUSB commit (3a3be3a1ebf0) added a shutdown callback
  for similar reasons (preventing SMMU-related crashes)

### 4. **Clear Side Effects**
The `dwc3_xlnx_remove` function performs standard cleanup:
- Depopulates child devices (`of_platform_depopulate`)
- Disables and unprepares clocks
- Manages runtime PM state

These are all safe operations for shutdown context.

### 5. **Meets Stable Criteria**
- **Fixes a real bug**: Prevents potential system instability during
  kexec
- **Small change**: Single line addition
- **Low risk**: Reuses existing, tested code path
- **No new features**: Pure bug fix
- **Clear benefit**: Improves system reliability during reboot/kexec
  operations

### 6. **Similar Issues in Other Drivers**
The pattern of missing shutdown callbacks causing issues during
kexec/reboot is well-documented in the kernel, particularly for devices
that perform DMA operations.

The fix ensures proper hardware shutdown sequence during system
reboot/shutdown, preventing the USB controller from accessing memory
after the system has started transitioning to a new kernel or shutting
down. This is especially important for systems using kexec for fast
reboots or crash dump collection.

 drivers/usb/dwc3/dwc3-xilinx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
index 4ca7f6240d07..09c3c5c226ab 100644
--- a/drivers/usb/dwc3/dwc3-xilinx.c
+++ b/drivers/usb/dwc3/dwc3-xilinx.c
@@ -422,6 +422,7 @@ static const struct dev_pm_ops dwc3_xlnx_dev_pm_ops = {
 static struct platform_driver dwc3_xlnx_driver = {
 	.probe		= dwc3_xlnx_probe,
 	.remove		= dwc3_xlnx_remove,
+	.shutdown	= dwc3_xlnx_remove,
 	.driver		= {
 		.name		= "dwc3-xilinx",
 		.of_match_table	= dwc3_xlnx_of_match,
-- 
2.39.5