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SubjectRe: [PATCH] mhi: add MHI_STATE_M2 to resume success criteria

The patch subject should be,

"bus: mhi: Wait for M2 state during system resume"

We follow "bus: mhi:" prefix for all MHI patches. Also, the subject should
clearly portray what the patch is intend to do.

On Tue, Apr 20, 2021 at 11:53:39AM +0800, Baochen Qiang wrote:
> During system resume, mhi driver triggers M3->M0 transition and then waits

s/mhi driver/MHI host

> for target device to enter M0 state. Once done, the device queues a state
> change event into ctrl event ring and notify mhi dirver by raising an

s/notify/notifies and s/mhi dirver/MHI host. MHI driver is somewhat confusing
since we have the MHI device driver (QRTR etc...) as well. So just use MHI host

> interrupt, where a tasklet is scheduled to process this event. In most cases,
> the taklet is served timely and wait operation succeeds.


> However, there are cases where CPU is busy and can not serve this tasklet

a/can not/cannot

> for some time. Once delay goes long enough, the device moves itself to M1
> state and also interrupts mhi driver after inserting a new state change
> event to ctrl ring. Later CPU finally has time to process the ring, however
> there are two events in it now:
> 1. for M3->M0 event, which is processed first as queued first,
> tasklet handler updates device state to M0 and wakes up the task,
> i.e., the mhi driver.
> 2. for M0->M1 event, which is processed later, tasklet handler
> triggers M1->M2 transition and updates device state to M2 directly,
> then wakes up the mhi driver(if still sleeping on this wait queue).
> Note that although mhi driver 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 driver has to keep waiting till timeout cause the M0 state
> has been 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
> Signed-off-by: Baochen Qiang <>

Could you please add a fixes tag as well? And this patch should be backported to
stable kernels also, so please CC


> ---
> 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 ce73cfa63cb3..ca5f2feed9d5 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -900,6 +900,7 @@ 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));
> --
> 2.25.1

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