Re: [PATCH v2] usb: dwc3: Trigger a GCTL soft reset when switching modes in DRD

[John Stultz]

On Wed, Oct 21, 2020 at 6:17 PM Thinh Nguyen <Thinh.Nguyen@xxxxxxxxxxxx> wrote:
>
> John Stultz wrote:
> > From: Yu Chen <chenyu56@xxxxxxxxxx>
> >
> > With the current dwc3 code on the HiKey960 we often see the
> > COREIDLE flag get stuck off in __dwc3_gadget_start(), which
> > seems to prevent the reset irq and causes the USB gadget to
> > fail to initialize.
> >
> > We had seen occasional initialization failures with older
> > kernels but with recent 5.x era kernels it seemed to be becoming
> > much more common, so I dug back through some older trees and
> > realized I dropped this quirk from Yu Chen during upstreaming
> > as I couldn't provide a proper rational for it and it didn't
> > seem to be necessary. I now realize I was wrong.
> >
> > After resubmitting the quirk Thinh Nguyen pointed out that it
> > shouldn't be a quirk and it is actually mentioned in the
> > programming guide that it should be done when switching modes
> > in DRD.
> >
> > So, to avoid these !COREIDLE lockups seen on HiKey960, this
> > patch issues GCTL soft reset when switching modes if the
> > controller is in DRD mode.
> >
> > Cc: Felipe Balbi <balbi@xxxxxxxxxx>
> > Cc: Tejas Joglekar <tejas.joglekar@xxxxxxxxxxxx>
> > Cc: Yang Fei <fei.yang@xxxxxxxxx>
> > Cc: YongQin Liu <yongqin.liu@xxxxxxxxxx>
> > Cc: Andrzej Pietrasiewicz <andrzej.p@xxxxxxxxxxxxx>
> > Cc: Thinh Nguyen <thinhn@xxxxxxxxxxxx>
> > Cc: Jun Li <lijun.kernel@xxxxxxxxx>
> > Cc: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: linux-usb@xxxxxxxxxxxxxxx
> > Signed-off-by: Yu Chen <chenyu56@xxxxxxxxxx>
> > Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
> > ---
> > v2:
> > * Rework to always call the GCTL soft reset in DRD mode,
> >   rather then using a quirk as suggested by Thinh Nguyen
> >
> > ---
> >  drivers/usb/dwc3/core.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> >
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index bdf0925da6b6..ca94f3a2a83c 100644
> > --- a/drivers/usb/dwc3/core.c
> > +++ b/drivers/usb/dwc3/core.c
> > @@ -114,10 +114,24 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
> >       dwc->current_dr_role = mode;
> >  }
> >
> > +static void dwc3_gctl_core_soft_reset(struct dwc3 *dwc)
> > +{
> > +     int reg;
> > +
> > +     reg = dwc3_readl(dwc->regs, DWC3_GCTL);
> > +     reg |= (DWC3_GCTL_CORESOFTRESET);
> > +     dwc3_writel(dwc->regs, DWC3_GCTL, reg);
> > +
> > +     reg = dwc3_readl(dwc->regs, DWC3_GCTL);
> > +     reg &= ~(DWC3_GCTL_CORESOFTRESET);
> > +     dwc3_writel(dwc->regs, DWC3_GCTL, reg);
> > +}
> > +
> >  static void __dwc3_set_mode(struct work_struct *work)
> >  {
> >       struct dwc3 *dwc = work_to_dwc(work);
> >       unsigned long flags;
> > +     int hw_mode;
> >       int ret;
> >       u32 reg;
> >
> > @@ -154,6 +168,11 @@ static void __dwc3_set_mode(struct work_struct *work)
> >               break;
> >       }
> >
> > +     /* Execute a GCTL Core Soft Reset when switch mode in DRD*/
> > +     hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
> > +     if (hw_mode == DWC3_GHWPARAMS0_MODE_DRD)
> > +             dwc3_gctl_core_soft_reset(dwc);
> > +
>
> I think this should be done inside the spin_lock.
>
> >       spin_lock_irqsave(&dwc->lock, flags);
> >
> >       dwc3_set_prtcap(dwc, dwc->desired_dr_role);
>
> The DRD mode change sequence should be like this if we want to switch
> from host -> device according to the programming guide (for all DRD IPs):
> 1. Reset controller with GCTL.CoreSoftReset
> 2. Set GCTL.PrtCapDir(device)
> 3. Soft reset with DCTL.CSftRst
> 4. Then follow up with the initializing registers sequence
>
> However, from code review, with this patch, it follows this sequence:
> a. Soft reset with DCTL.CSftRst on driver probe
> b. Reset controller with GCTL.CoreSoftReset
> c. Set GCTL.PrtCapDir(device)
> d. < missing DCTL.CSftRst >
> e. Then follow up with initializing registers sequence
>
> It may work, but it doesn't follow the programming guide.

Much appreciated for the guidance here. I don't believe I have access
to the programming guide (unless its publicly available somewhere?),
so I'm just working with what I can experimentally figure out and
vendor patch history.

So I'll try to translate the above into the driver as best I can, but
again, I really appreciate your review and corrections here!

thanks
-john