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Date:   Mon, 24 May 2021 11:14:58 +0800
From:   bqiang@codeaurora.org
To:     Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc:     hemantk@codeaurora.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, ath11k@lists.infradead.org
Subject: Re: [PATCH] mhi: add MHI_STATE_M2 to resume success criteria
In-Reply-To: <20210521124530.GF70095@thinkpad>
References: <20210420035339.282963-1-bqiang@codeaurora.org>
 <20210521124530.GF70095@thinkpad>
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On 2021-05-21 20:45, Manivannan Sadhasivam wrote:
> Hi,
> 
> 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
> everywhere.
> 
>> interrupt, where a tasklet is scheduled to process this event. In most 
>> cases,
>> the taklet is served timely and wait operation succeeds.
>> 
> 
> s/taklet/tasklet
> 
>> 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 <bqiang@codeaurora.org>
> 
> Could you please add a fixes tag as well? And this patch should be 
> backported to
> stable kernels also, so please CC stable@vger.kernel.org.
> 
> Thanks,
> Mani
> 

Thanks Mani.
Will address them and send as V2.

>> ---
>>  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
>>