[regression] mhi: ath11k resume fails on some devices

[Manivannan Sadhasivam]

On Thu, Sep 16, 2021 at 07:42:02PM +0300, Kalle Valo wrote:
> Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org> writes:
> 
> > On Thu, Sep 16, 2021 at 01:18:22PM +0200, Loic Poulain wrote:
> >> Le jeu. 16 sept. 2021 à 13:12, Manivannan Sadhasivam <
> >> manivannan.sadhasivam at linaro.org> a écrit :
> >> 
> >
> > [...]
> >
> >> > If things seems to work fine without that patch, then it implies that
> >> > setting M0
> >> > state works during resume. I think we should just revert that patch.
> >> >
> >> > Loic, did that patch fix any issue for you or it was a cosmetic fix only?
> >> 
> >> 
> >> It fixes sdx modem resuming issue, without that we don’t know modem needs
> >> to be reinitialized.
> >> 
> >
> > Okay. Then in that case, the recovery mechanism has to be added to the ath11k
> > MHI controller.
> 
> What does that mean in practise, do you have any pointers or examples? I
> have no clue what you are proposing :)
> 

Take a look at the mhi_pci_recovery_work() function below:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/bus/mhi/pci_generic.c#n610

You need to implement something similar that basically powers up the MHI
endpoint (QCA6390) in case pm_resume() fails. At minimum, you need to call
below functions:

# Check if the device is powered on. If yes, then power it down to bring it back
mhi_power_down()
mhi_unprepare_after_power_down()

# Power up the device
mhi_prepare_for_power_up()
mhi_sync_power_up()

This implies that the WLAN device has been powered off during suspend, so the
resume fails and we are bringing the device back to working state.

> > If that's too much of work for Kalle, then I'll look into it. But I might get
> > time only after Plumbers.
> 
> I'm busy, as always, so not sure when I'm able to do it either. I think
> we should seriously consider reverting 020d3b26c07a and adding it back
> after ath11k is able to handle this new situation.
> 

Since Loic said that reverting would cause his modem (SDX device) to fail during
resume, this is not possible.

Thanks,
Mani

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