linux-kernel - RE: [EXT] Re: [PATCH v1] usb: dwc3: remove the call trace of USBx

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Date:   Tue, 27 Aug 2019 02:37:45 +0000
From:   Ran Wang <ran.wang_1@....com>
To:     Felipe Balbi <balbi@...nel.org>, Yinbo Zhu <yinbo.zhu@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
CC:     Xiaobo Xie <xiaobo.xie@....com>, Jiafei Pan <jiafei.pan@....com>
Subject: RE: [EXT] Re: [PATCH v1] usb: dwc3: remove the call trace of
 USBx_GFLADJ

Hi Felipe,

On Thursday, August 15, 2019 13:59, Felipe Balbi wrote:
> 
> Hi,
> 
> Yinbo Zhu <yinbo.zhu@....com> writes:
> >> Yinbo Zhu <yinbo.zhu@....com> writes:
> >> >> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> >> >> > index
> >> >> > 98bce85c29d0..a133d8490322 100644
> >> >> > --- a/drivers/usb/dwc3/core.c
> >> >> > +++ b/drivers/usb/dwc3/core.c
> >> >> > @@ -300,8 +300,7 @@ static void
> >> >> > dwc3_frame_length_adjustment(struct
> >> >> > dwc3 *dwc)
> >> >> >
> >> >> >       reg = dwc3_readl(dwc->regs, DWC3_GFLADJ);
> >> >> >       dft = reg & DWC3_GFLADJ_30MHZ_MASK;
> >> >> > -     if (!dev_WARN_ONCE(dwc->dev, dft == dwc->fladj,
> >> >> > -         "request value same as default, ignoring\n")) {
> >> >> > +     if (dft != dwc->fladj) {
> >> >>
> >> >> if the value isn't different, why do you want to change it?
> >> >>
> >> >> --
> >> >> Balbi
> >> > Hi Balbi,
> >> >
> >> > I don't change any value. I was remove that call trace.
> >>
> >> Sure you do. The splat only shows when you request a FLADJ value
> >> that's the same as the one already in the register. The reason you
> >> see the splat is because your requested value is what's already in the HW.
> >>
> >> So, again, why are you adding this device tree property if the value
> >> is already the correct one?
> >>
> >> > In addition that GFLADJ_30MHZ value intial value is 0, and it's
> >> > value must be 0x20, if not, usb will not work.
> >>
> >> it's not zero, otherwise the splat wouldn't trigger. You're
> >> requesting the value that's already in your register by default.
> >>
> >> --
> >> Balbi
> >
> > Hi Balbi,
> >
> > According that rm doc that GFLADJ_30MHZ has a default value is 0x20,
> > when GFLADJ_30MHZ_REG_SEL is 0, this 0x20 is a hard-coded value.
> >
> > But in fact, that default value is 0, please you note!
> >
> > Then according that xhci spec 5.2.4, that register the sixth bit if is
> > 0, then that can support Frame Lenth Timing value.
> >
> > So set GFLADJ_30MHZ_REG_SEL to 1 for use FLADJ, then I find that it
> > must use 0x20 usb will work well, even thoug xhci can permit
> > GFLADJ_30MHZ use other value
> 
> You only get the splat because you try to sent GFLADJ to 0x20 and it's ALREADY
> 0x20. This means that you don't need the property in DTS.
> 
> > In addition about what you said is about dts patch, and that patch had
> > merged by upstream, patch owner isn't me,
> 
> Well, then remove the setting from DTS, since clearly it's not needed.

Please considering below scenarios on the same board which needs GFLADJ property on kernel DTS:

1. Board boot to U-Boot first, then load kernel. In this case, we need kernel DTS
    help to get GFLADJ setting right, everything is as expected.

2. Board boot to U-Boot console, then execute 'usb start' under U-Boot console to init
    DWC3 controller, then load kernel. In this case, actually GFLADJ is correctly
    configured already, and the GFLADJ config double-checking is fine (because kernel
    cannot know if U-Boot has initialized it or not), but warning looks not necessary.

3. Board boot to kernel, GFLADJ get set from DTS, then system suspend & resume. In this case
    when resuming, GFLADJ setting has been restored correctly, so here we might not need
    send out the warning message (double-checking might be fine).

So, what's your suggestion to remove this looks non-necessary warning message?

Thanks & Regards,
Ran

> > My patch is only for remove the call-trace, about why remove it commit
> > information has detail introduce please check!
> 
> --
> balbi