From: Baochen Qiang bqiang@codeaurora.org

During system resume, MHI host triggers M3->M0 transition and then waits for target device to enter M0 state. Once done, the device queues a state change event into ctrl event ring and notifies MHI host by raising an interrupt, where a tasklet is scheduled to process this event. In most cases, the tasklet is served timely and wait operation succeeds.

However, there are cases where CPU is busy and cannot serve this tasklet for some time. Once delay goes long enough, the device moves itself to M1 state and also interrupts MHI host after inserting a new state change event to ctrl ring. Later when CPU finally has time to process the ring, there will be two events:

1. For M3->M0 event, which is the first event to be processed queued first. The tasklet handler serves the event, updates device state to M0 and wakes up the task.

2. For M0->M1 event, which is processed later, the tasklet handler triggers M1->M2 transition and updates device state to M2 directly, then wakes up the MHI host (if it is still sleeping on this wait queue).

Note that although MHI host has been woken up while processing the first event, it may still has no chance to run before the second event is processed. In other words, MHI host has to keep waiting till timeout causing the M0 state to be missed.

kernel log here: ... Apr 15 01:45:14 test-NUC8i7HVK kernel: [ 4247.911251] mhi 0000:06:00.0: Entered with PM state: M3, MHI state: M3 Apr 15 01:45:14 test-NUC8i7HVK kernel: [ 4247.917762] mhi 0000:06:00.0: State change event to state: M0 Apr 15 01:45:14 test-NUC8i7HVK kernel: [ 4247.917767] mhi 0000:06:00.0: State change event to state: M1 Apr 15 01:45:14 test-NUC8i7HVK kernel: [ 4338.788231] mhi 0000:06:00.0: Did not enter M0 state, MHI state: M2, PM state: M2 ...

Fix this issue by simply adding M2 as a valid state for resume.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1

Cc: stable@vger.kernel.org Fixes: 0c6b20a1d720 ("bus: mhi: core: Add support for MHI suspend and resume") Signed-off-by: Baochen Qiang bqiang@codeaurora.org Reviewed-by: Hemant Kumar hemantk@codeaurora.org Reviewed-by: Manivannan Sadhasivam manivannan.sadhasivam@linaro.org Link: https://lore.kernel.org/r/20210524040312.14409-1-bqiang@codeaurora.org [mani: slightly massaged the commit message] Signed-off-by: Manivannan Sadhasivam manivannan.sadhasivam@linaro.org --- drivers/bus/mhi/core/pm.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c index 704a5e225097..bbf6cd04861e 100644 --- a/drivers/bus/mhi/core/pm.c +++ b/drivers/bus/mhi/core/pm.c @@ -926,6 +926,7 @@ int mhi_pm_resume(struct mhi_controller *mhi_cntrl)

ret = wait_event_timeout(mhi_cntrl->state_event, mhi_cntrl->dev_state == MHI_STATE_M0 || + mhi_cntrl->dev_state == MHI_STATE_M2 || MHI_PM_IN_ERROR_STATE(mhi_cntrl->pm_state), msecs_to_jiffies(mhi_cntrl->timeout_ms));