From: Michael Grzeschik m.grzeschik@pengutronix.de
[ Upstream commit af076a41f8a28faf9ceb9dd2d88aef2c202ef39a ]
It is possible that the gadget will be disabled, while the udc is suspended. When enabling the udc in that case, the clock gating will not be enabled again. Leaving the phy unclocked. Even when the udc is not enabled, connecting this powered but not clocked phy leads to enumeration errors on the host side.
To ensure that the clock gating will be in an valid state, we ensure that the clock gating will be enabled before stopping the udc.
Signed-off-by: Michael Grzeschik m.grzeschik@pengutronix.de Acked-by: Minas Harutyunyan hminas@synopsys.com Link: https://lore.kernel.org/r/20250417-dwc2_clock_gating-v1-1-8ea7c4d53d73@pengu... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis of the code, similar commits, and the context, here is my assessment:
**YES**
This commit should be backported to stable kernel trees. Here's my extensive analysis:
## Code Analysis
The commit adds clock gating exit logic to the `dwc2_hsotg_udc_stop()` function in drivers/usb/dwc2/gadget.c. Specifically, it adds these lines before shutting down endpoints:
```c /* Exit clock gating when driver is stopped. */ if (hsotg->params.power_down == DWC2_POWER_DOWN_PARAM_NONE && hsotg->bus_suspended && !hsotg->params.no_clock_gating) { dwc2_gadget_exit_clock_gating(hsotg, 0); } ```
## Rationale for Backporting
1. **Follows Established Pattern**: The code change exactly matches the pattern used throughout the dwc2 driver in other similar contexts. I found identical condition checks and dwc2_gadget_exit_clock_gating() calls in: - `drivers/usb/dwc2/platform.c:333-336` (driver removal) - `drivers/usb/dwc2/core_intr.c:314-317` (session request interrupt) - `drivers/usb/dwc2/core_intr.c:447-450` (wakeup detected interrupt) - `drivers/usb/dwc2/gadget.c:3738-3741` (USB reset detect interrupt)
2. **Fixes a Real Bug**: The commit message describes a specific hardware state issue: "Even when the udc is not enabled, connecting this powered but not clocked phy leads to enumeration errors on the host side." This indicates a functional problem that affects users.
3. **Low Risk, High Consistency**: The fix simply adds the same clock gating exit pattern that already exists in 4+ other locations in the same driver. This demonstrates it's a well-tested, safe pattern.
4. **Critical Hardware State Management**: Clock gating is a fundamental power management feature, and incorrect state handling can cause system hangs or hardware enumeration failures, as evidenced by the related fix in commit 2c6b6afa59e7 which had to be marked for stable.
5. **Matches Historical Precedent**: Looking at the reference commits: - Similar Commit #2 (YES): "usb: dwc2: gadget: Fix exiting from clock gating" - This shows clock gating exit fixes are considered backport-worthy - Similar Commit #3 (YES): "usb: dwc2: do not gate off the hardware if it does not support clock gating" - This reinforces that clock gating correctness is critical
6. **Stable Tree Criteria Met**: - ✅ Fixes important bug (PHY enumeration errors) - ✅ Small and contained change (6 lines) - ✅ No architectural changes - ✅ Minimal regression risk (uses existing, proven pattern) - ✅ Confined to dwc2 subsystem
7. **Recent Historical Context**: The git history shows multiple recent clock gating fixes that were marked for stable (31f42da31417, 2c6b6afa59e7), indicating this subsystem area is actively maintained and these types of fixes are important for stable trees.
The commit addresses a state consistency issue where the clock gating state becomes invalid when the UDC is stopped while suspended, leading to hardware enumeration problems. This is exactly the type of subtle but important hardware state management bug that stable trees are designed to fix.
drivers/usb/dwc2/gadget.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c index bd4c788f03bc1..d3d0d75ab1f59 100644 --- a/drivers/usb/dwc2/gadget.c +++ b/drivers/usb/dwc2/gadget.c @@ -4604,6 +4604,12 @@ static int dwc2_hsotg_udc_stop(struct usb_gadget *gadget) if (!hsotg) return -ENODEV;
+ /* Exit clock gating when driver is stopped. */ + if (hsotg->params.power_down == DWC2_POWER_DOWN_PARAM_NONE && + hsotg->bus_suspended && !hsotg->params.no_clock_gating) { + dwc2_gadget_exit_clock_gating(hsotg, 0); + } + /* all endpoints should be shutdown */ for (ep = 1; ep < hsotg->num_of_eps; ep++) { if (hsotg->eps_in[ep])