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

[Hemant Kumar]

On 4/19/21 8:53 PM, Baochen Qiang wrote:
> During system resume, mhi driver 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 notify mhi dirver by raising an
> 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
> 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 <bqiang@xxxxxxxxxxxxxx>

nice explanation of the issue!

Reviewed-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>

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