Re: [PATCH v2 2/3] net: qrtr: support suspend/hibernation

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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@xxxxxxxxxxx>

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

Could you please confirm if this patch can be applied separately and won't cause
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

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

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