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Message-ID: <bb25f9cb-720e-4b53-950c-41eddc19da59@quicinc.com>
Date: Tue, 27 Feb 2024 18:02:01 +0800
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Subject: Re: [PATCH v2 2/3] net: qrtr: support suspend/hibernation
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To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
CC: <ath11k@lists.infradead.org>, <linux-wireless@vger.kernel.org>,
        <linux-arm-msm@vger.kernel.org>, <mhi@lists.linux.dev>
References: <20240227063613.4478-1-quic_bqiang@quicinc.com>
 <20240227063613.4478-3-quic_bqiang@quicinc.com>
 <20240227071531.GD2587@thinkpad>
 <7b743820-850a-4871-a0d8-aded36e11aba@quicinc.com>
 <20240227095602.GK2587@thinkpad>
From: Baochen Qiang <quic_bqiang@quicinc.com>
In-Reply-To: <20240227095602.GK2587@thinkpad>
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On 2/27/2024 5:56 PM, Manivannan Sadhasivam wrote:
> On Tue, Feb 27, 2024 at 04:39:41PM +0800, Baochen Qiang wrote:
>>
>>
>> On 2/27/2024 3:15 PM, Manivannan Sadhasivam wrote:
>>> On Tue, Feb 27, 2024 at 02:36:12PM +0800, Baochen Qiang wrote:
>>>> MHI devices may not be destroyed during suspend/hibernation, so need
>>>> to unprepare/prepare MHI channels throughout the transition, this is
>>>> done by adding suspend/resume callbacks.
>>>>
>>>> The suspend callback is called in the late suspend stage, this means
>>>> MHI channels are still alive at suspend stage, and that makes it
>>>> possible for an MHI controller driver to communicate with others over
>>>> those channels at suspend stage. While the resume callback is called
>>>> in the early resume stage, for a similar reason.
>>>>
>>>> Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.30
>>>>
>>>> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
>>>
>>> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>>>
>>> Could you please confirm if this patch can be applied separately and won't cause
>>> regression?
>> Just searched the kernel and found another two drivers using IPCR channels,
>> one is pci_epf_mhi_driver in drivers/pci/endpoint/functions/pci-epf-mhi.c
>> and the other is mhi_pci_driver in drivers/bus/mhi/host/pci_generic.c.
>>
>> For pci_epf_mhi_driver, this is not impacted because the devices for those
>> channels are attached to mhi_ep_bus_type while QRTR MHI driver attached to
>> mhi_bus_type.
>>
>> For mhi_pci_driver, I am afraid there would be regressions caused by this
>> patch. The regression is because when system suspends, mhi_pci_suspend() is
>> called and then qcom_mhi_qrtr_pm_suspend_late() called, however the latter
>> would fail because MHI is moved to M3 state by call mhi_pm_suspend() in
>> mhi_pci_suspend(). To address this, there might be two options: the first is
>> to move mhi_pci_suspend() to a late suspend stage which would be called
>> after qcom_mhi_qrtr_pm_suspend_late(). and the second is to avoid whole QRTR
>> suspend operation in such cases. I prefer the second one, because if MHI is
>> going to suspend, instead of power down, it is pointless to unprepare MHI
>> channels and re-prepare them after resume back. We can achieve this purpose
>> by adding a status_cb() to QRTR MHI driver which would be called when MHI
>> goes to low power mode. And then QRTR MHI driver could decide not to
>> suspend/resume if low power mode is notified.
>>
>> Your thoughts?
>>
> 
> I'd rather query the MHI state of the device in suspend/resume callback using
> mhi_get_mhi_state(mhi_dev->mhi_cntrl) and if the device is found to be in M3
> (suspend) state, then I'd skip prepare/unprepare part.
> 
> Because this makes it clear that, if the device is in suspend state, then no
> need for the client drivers to unprepare/prepare the channels.
> 
Sounds reasonable, will do accordingly in v3.

> - Mani
>