Re: [PATCH] USB: DWC2: Add VBUS overcurrent detection control.

[Paul Cercueil]

Hi Greg,

Le mar., juin 15 2021 at 11:48:30 +0200, Greg KH 
<gregkh@xxxxxxxxxxxxxxxxxxx> a écrit :
> On Tue, Jun 15, 2021 at 09:52:20AM +0100, Paul Cercueil wrote:
> >  Hi Zhou,
> >
> >  Le mar., juin 15 2021 at 16:16:39 +0800, 周琰杰 
> > <zhouyanjie@xxxxxxxxxxxxxx>
> >  a écrit :
> >  > Hi Greg,
> >  >
> >  > Sorry for taking so long to reply.
> >  >
> >  > 于 Tue, 23 Mar 2021 16:31:29 +0100
> >  > Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 写道:
> >  >
> >  > >  On Tue, Mar 23, 2021 at 11:24:26PM +0800, 周琰杰 (Zhou 
> > Yanjie)
> >  > > wrote:
> >  > >  > Introduce configurable option for enabling GOTGCTL register
> >  > >  > bits VbvalidOvEn and VbvalidOvVal. Once selected it disables
> >  > >  > VBUS overcurrent detection.
> >  > >  >
> >  > >  > This patch is derived from Dragan Čečavac (in the kernel 
> > 3.18
> >  > >  > tree of CI20). It is very useful for the MIPS Creator 
> > CI20(r1).
> >  > >  > Without this patch, CI20's OTG port has a great probability 
> > to
> >  > >  > face overcurrent warning, which breaks the OTG functionality.
> >  > >  >
> >  > >  > Signed-off-by: 周琰杰 (Zhou Yanjie) 
> > <zhouyanjie@xxxxxxxxxxxxxx>
> >  > >  > Signed-off-by: Dragan Čečavac <dragancecavac@xxxxxxxxx>
> >  > >  > ---
> >  > >  >  drivers/usb/dwc2/Kconfig | 6 ++++++
> >  > >  >  drivers/usb/dwc2/core.c  | 9 +++++++++
> >  > >  >  2 files changed, 15 insertions(+)
> >  > >  >
> >  > >  > diff --git a/drivers/usb/dwc2/Kconfig 
> > b/drivers/usb/dwc2/Kconfig
> >  > >  > index c131719..e40d187 100644
> >  > >  > --- a/drivers/usb/dwc2/Kconfig
> >  > >  > +++ b/drivers/usb/dwc2/Kconfig
> >  > >  > @@ -94,4 +94,10 @@ config USB_DWC2_DEBUG_PERIODIC
> >  > >  >  	  non-periodic transfers, but of course the debug logs
> >  > >  > will be incomplete. Note that this also disables some debug
> >  > > messages
> >  > >  >  	  for which the transfer type cannot be deduced.
> >  > >  > +
> >  > >  > +config USB_DWC2_DISABLE_VOD
> >  > >  > +	bool "Disable VBUS overcurrent detection"
> >  > >  > +	help
> >  > >  > +	  Say Y here to switch off VBUS overcurrent detection. It
> >  > >  > enables USB
> >  > >  > +	  functionality blocked by overcurrent detection.
> >  > >
> >  > >  Why would this be a configuration option?  Shouldn't this be 
> > dynamic
> >  > >  and just work properly automatically?
> >  > >
> >  > >  You should not have to do this on a build-time basis, it 
> > should be
> >  > >  able to be detected and handled properly at run-time for all
> >  > > devices.
> >  > >
> >  >
> >  > I consulted the original author Dragan Čečavac, he think since 
> > this is
> >  > a feature which disables overcurrent detection, so we are not 
> > sure if
> >  > it could be harmful for some devices. Therefore he advise against
> >  > enabling it in runtime, and in favor that user explicitely has to
> >  > enable it.
> >
> >  This could still be enabled at runtime, though, via a module 
> > parameter.
> >  Leave it enabled by default, and those who want to disable it can 
> > do it.
>
> This is not the 1990's, please NEVER add new module parameters,

First time I hear this.

> especially ones that are somehow supposed to be device-specific.
>
> Remember, module options are code-wide, not device-specific.

Right. I thought "just make the option available on devices that 
support it" but that's not how it works.

-Paul

> Just do this based on the device type, or something else dynamic, do 
> NOT
> make this be forced to be selected by a kernel configuration option 
> or a
> random module option at runtime.
>
> thanks,
>
> greg k-h