Re: [PATCH v2] bus: mhi: Wait for M2 state during system resume

[Manivannan Sadhasivam]

On Mon, May 24, 2021 at 12:03:12PM +0800, Baochen Qiang wrote:
> 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 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 host.
> 	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 host(if 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 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
> 
> Fixes: 0c6b20a1d720 ("bus: mhi: core: Add support for MHI suspend and resume")
> Signed-off-by: Baochen Qiang <bqiang@xxxxxxxxxxxxxx>
> Reviewed-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>

Thanks,
Mani

> ---
>  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 e2e59a341fef..59b009a3ee9b 100644
> --- a/drivers/bus/mhi/core/pm.c
> +++ b/drivers/bus/mhi/core/pm.c
> @@ -934,6 +934,7 @@ 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
>