Re: [PATCH] usb:typec:tcpm:support double Rp to Vbus cable as sink

[Michael Wu]

On 2023/9/18 22:22, Guenter Roeck wrote:
> On 9/18/23 03:31, Heikki Krogerus wrote:
> > On Thu, Sep 14, 2023 at 08:31:54AM +0800, Michael Wu wrote:
> > > The USB Type-C Cable and Connector Specification defines the wire
> > > connections for the USB Type-C to USB 2.0 Standard-A cable assembly
> > > (Release 2.2, Chapter 3.5.2).
> > > The Notes says that Pin A5 (CC) of the USB Type-C plug shall be 
> > > connected
> > > to Vbus through a resister Rp.
> > > However, there is a large amount of such double Rp connected to Vbus
> > > non-standard cables which produced by UGREEN circulating on the 
> > > market, and
> > > it can affects the normal operations of the state machine easily,
> > > especially to CC1 and CC2 be pulled up at the same time.
> > > In fact, we can regard those cables as sink to avoid abnormal state.
> > >
> > > Message as follow:
> > > [   58.900212] VBUS on
> > > [   59.265433] CC1: 0 -> 3, CC2: 0 -> 3 [state TOGGLING, polarity 0, 
> > > connected]
> > > [   62.623308] CC1: 3 -> 0, CC2: 3 -> 0 [state TOGGLING, polarity 0, 
> > > disconnected]
> > > [   62.625006] VBUS off
> > > [   62.625012] VBUS VSAFE0V
> > >
> > > Signed-off-by: Michael Wu <michael@xxxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/usb/typec/tcpm/tcpm.c | 3 ++-
> > >   1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/usb/typec/tcpm/tcpm.c 
> > > b/drivers/usb/typec/tcpm/tcpm.c
> > > index d962f67c95ae6..beb7143128667 100644
> > > --- a/drivers/usb/typec/tcpm/tcpm.c
> > > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > > @@ -519,7 +519,8 @@ static const char * const pd_rev[] = {
> > >   #define tcpm_port_is_sink(port) \
> > >       ((tcpm_cc_is_sink((port)->cc1) && 
> > > !tcpm_cc_is_sink((port)->cc2)) || \
> > > -     (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1)))
> > > +     (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1)) 
> > > || \
> > > +     (tcpm_cc_is_sink((port)->cc1) && tcpm_cc_is_sink((port)->cc2)))
> > >   #define tcpm_cc_is_source(cc) ((cc) == TYPEC_CC_RD)
> > >   #define tcpm_cc_is_audio(cc) ((cc) == TYPEC_CC_RA)
> >
> > This look OK to me, but I would still like to wait for comments from
> > Guenter - just in case.
>
> Look at the conditions. Reordered, we end up with
>      (tcpm_cc_is_sink((port)->cc1) && !tcpm_cc_is_sink((port)->cc2)) ||
>      (tcpm_cc_is_sink((port)->cc1) && tcpm_cc_is_sink((port)->cc2))
> which simplifies to
>      tcpm_cc_is_sink((port)->cc1)
> making the complete expression
>      tcpm_cc_is_sink((port)->cc1) ||
>      (tcpm_cc_is_sink((port)->cc2) && !tcpm_cc_is_sink((port)->cc1))
> which simplifies further to
>      tcpm_cc_is_sink((port)->cc1) || tcpm_cc_is_sink((port)->cc2)
>
> The simplified expression doesn't conflict with other detections, so I am
> ok with it. It might be worthwhile adding a comment to the code, though,
> explaining the reason
> Guenter
>
> > thanks,
Dear Guenter,

I have modified it according to your opinion, and resend it as patch 
v2[1]. Please review.

[1] 
https://lore.kernel.org/all/20230920063030.66312-1-michael@xxxxxxxxxxxxxxxxx/

--
Regards,
Michael Wu