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

[Guenter Roeck]

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,