linux-kernel - Re: [PATCH 0/5] usb: dwc3: qcom: Allow runtime PM

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Date:   Mon, 27 Mar 2023 15:40:55 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     andersson@...nel.org, Thinh.Nguyen@...opsys.com,
        gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/5] usb: dwc3: qcom: Allow runtime PM

On Mon, Mar 27, 2023 at 11:24:58AM +0200, Konrad Dybcio wrote:
> 
> 
> On 27.03.2023 11:17, Manivannan Sadhasivam wrote:
> > On Mon, Mar 27, 2023 at 11:01:35AM +0200, Konrad Dybcio wrote:
> >>
> >>
> >> On 25.03.2023 17:52, Manivannan Sadhasivam wrote:
> >>> Hi,
> >>>
> >>> This series allows the dwc3-qcom driver to do runtime PM itself without
> >>> userspace intervention. Still, userspace is required to enable runtime PM
> >>> for dwc3 glue and xhci drivers as we cannot enable runtime PM for them.
> >>> But this series avoids one more additional step.
> >> What sort of 'userspace intervention' are we talking about?
> >> echo mem > /sys/power/state?
> >>
> > 
> > I forgot to add that bit:
> > 
> > echo auto > /sys/devices/platform/soc@...8f8800.usb/a800000.usb/xhci-hcd.1.auto/power/control
> > echo auto > /sys/devices/platform/soc@...8f8800.usb/a800000.usb/power/control
> > 
> > You need to set "auto" for the runtime control for both xhci and dwc drivers.
> > 
> > Then if you don't connect a usb device, all 3 drivers (dwc3-qcom, dwc3, and
> > xhci) will become runtime suspended after a delay of 5s (default delay).
> > 
> > This can be confirmed by:
> > 
> > cat /sys/devices/platform/soc@...8f8800.usb/power/runtime_status
> > 
> > After connecting a usb device, they will all become "active".
> Thanks! And if I'm following correctly, we can't enable runtime PM
> for the DWC3 glue and XHCI drivers, as that would cause havoc on
> other, non-qc platforms. Is that correct?
> 

Kind of. Actually dwc3 glue is our qcom driver, other one is just dwc3 driver.

The havoc would apply to xhci driver because, once it is suspended, one of its
parent drivers has to resume it. And that requires runtime PM support for all
the parent drivers which is currently not available.

But for dwc3 driver, I'm not sure about the consequence though. Maybe I should
send it as a separate patch later on and see what other platforms folks think
of it.

Thanks,
Mani

> Konrad
> > 
> > Thanks,
> > Mani
> > 
> >> Konrad
> >>>
> >>> While enabling runtime PM, I noticed that the xhci driver suspends before
> >>> catching the xhci interrupts during resume. This ended up deferring the
> >>> device enumeration for some time. So I included a patch adding autosuspend
> >>> delay of 200ms to the xhci driver. With this delay, usb enumeration happens
> >>> properly.
> >>>
> >>> This series has been tested on SC8280XP-CRD and RB5 devices.
> >>>
> >>> Thanks,
> >>> Mani
> >>>
> >>> Manivannan Sadhasivam (5):
> >>>   arm64: dts: qcom: sc8280xp: Add missing dwc3 quirks
> >>>   xhci: host: Use 200ms autosuspend delay for runtime suspend
> >>>   usb: dwc3: qcom: Fix null ptr access during runtime_suspend()
> >>>   usb: dwc3: qcom: Clear pending interrupt before enabling wake
> >>>     interrupt
> >>>   usb: dwc3: qcom: Allow runtime PM
> >>>
> >>>  arch/arm64/boot/dts/qcom/sc8280xp.dtsi | 14 ++++++++++++++
> >>>  drivers/usb/dwc3/dwc3-qcom.c           | 13 +++++++++----
> >>>  drivers/usb/host/xhci-plat.c           |  2 ++
> >>>  3 files changed, 25 insertions(+), 4 deletions(-)
> >>>
> > 

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