Re: [PATCH 3/3] clk: qcom: gcc-sc7280: Update the .pwrsts for usb gdsc

[Krishna Kurapati PSSNV]

On 9/14/2022 2:37 PM, Johan Hovold wrote:
> [ Please try to wrap your replies at 72 columns or so. ]
>
> On Wed, Sep 14, 2022 at 02:28:31PM +0530, Rajendra Nayak wrote:
> > On 9/14/2022 2:07 PM, Krishna Kurapati PSSNV wrote:
> > > On 9/14/2022 12:39 PM, Johan Hovold wrote:
> > > > On Thu, Sep 01, 2022 at 03:47:56PM +0530, Rajendra Nayak wrote:
> > > > > USB on sc7280 cannot support wakeups from low power states
> > > > > if the GDSC is turned OFF. Update the .pwrsts for usb GDSC so it
> > > > > only transitions to RET in low power.
> > > >
> > > > It seems this isn't just needed for wakeup to work. On both sc7280 and
> > > > sc8280xp the controller doesn't resume properly if the domain has been
> > > > powered off (i.e. regardless of whether wakeup is enabled or not).
> > > Hi Johan,
> > >
> > >     I believe you are referring to the reinit that happens in xhci resume path after wakeup happens:
> > >
> > > [   48.675839] xhci-hcd xhci-hcd.14.auto: xHC error in resume, USBSTS 0x411, Reinit
> > >
> > > I see that when USB GDSC is not in retention, we don't retain controller state and go for reinit and re-enum of connected devices. We are seeing an additional delay of around ~0.7 sec (in chromebooks running on SC7280) in the wakeup path for re-enumeration of connected USB devices. To avoid this, we wanted to put GDSC in retention during PM suspend.
> >
> > ok, so perhaps the commit msg should be updated to something like
> >
> > 'USB on sc7280 needs to prevent the GDSC from being turned OFF for a couple of reasons
> > 1. To prevent re-init and re-enumeration of all connected devices resulting in additional delay coming out of low power states
> > 2. To support wakeups from connected devices from low power states'
>
> The fundamental issue here is that state is lost during suspend which
> the driver doesn't currently (or can not) restore. Doesn't hurt to
> mention the specific consequences you list above as well.
>
> > > > Are you sure there's no state that needs to be retained regardless of
> > > > the wakeup setting?
> > > >
> > > > > Signed-off-by: Rajendra Nayak <quic_rjendra@xxxxxxxxxxx>
> > > > > ---
> > > > >    drivers/clk/qcom/gcc-sc7280.c | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/clk/qcom/gcc-sc7280.c b/drivers/clk/qcom/gcc-sc7280.c
> > > > > index 7ff64d4d5920..de29a034e725 100644
> > > > > --- a/drivers/clk/qcom/gcc-sc7280.c
> > > > > +++ b/drivers/clk/qcom/gcc-sc7280.c
> > > > > @@ -3126,7 +3126,7 @@ static struct gdsc gcc_usb30_prim_gdsc = {
> > > > >        .pd = {
> > > > >            .name = "gcc_usb30_prim_gdsc",
> > > > >        },
> > > > > -    .pwrsts = PWRSTS_OFF_ON,
> > > > > +    .pwrsts = PWRSTS_RET_ON,
> > > > >        .flags = VOTABLE,
> > > > >    };
> > > >
> > > > And what about gcc_usb30_sec_gdsc?
> > >
> > > Currently wakeup is not enabled on secondary controller as its not required for end product platform (herobrine variant). So leaving the usb30_sec_gdsc as it is for now.
> >
> > It perhaps makes sense to update that as well, and given this is a compute specific chipset and we dont have to worry about
> > USB in device mode, its safe to assume if and when that controller is used (in future designs) it would only support host mode?
>
> What would be the problem when using the controller in peripheral mode?
> Don't you want to retain the controller state when suspended also in
> that case?
Hi Johan. You're right. When peripheral bus suspend lands in, we might 
need to keep GDSC ON in device mode as well.

Regards,
Krishna,