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Date:   Mon, 24 May 2021 09:01:49 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Baochen Qiang <bqiang@codeaurora.org>
Cc:     manivannan.sadhasivam@linaro.org, hemantk@codeaurora.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        ath11k@lists.infradead.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] bus: mhi: Wait for M2 state during system resume
Message-ID: <YKtPXWrTb6Qj+E9l@kroah.com>
References: <20210524040312.14409-1-bqiang@codeaurora.org>
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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@codeaurora.org>
> Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
> ---
>  drivers/bus/mhi/core/pm.c | 1 +
>  1 file changed, 1 insertion(+)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>