linux-kernel - Re: [PATCH v3 1/4] usb: typec: Use Thunderbolt 3 cable discover mode VDO in Enter

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Message-ID: <20201120085250.GD4120550@kuha.fi.intel.com>
Date:   Fri, 20 Nov 2020 10:52:50 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     Utkarsh Patel <utkarsh.h.patel@...el.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        enric.balletbo@...labora.com, rajmohan.mani@...el.com,
        azhar.shaikh@...el.com
Subject: Re: [PATCH v3 1/4] usb: typec: Use Thunderbolt 3 cable discover mode
 VDO in Enter_USB message

On Fri, Nov 20, 2020 at 12:36:25AM -0800, Prashant Malani wrote:
> On Fri, Nov 20, 2020 at 10:05:14AM +0200, Heikki Krogerus wrote:
> > On Wed, Nov 18, 2020 at 10:32:08PM -0800, Utkarsh Patel wrote:
> > > When Thunderbolt 3 cable is being used to create USB4 connection, use
> > > Thunderbolt 3 discover mode VDO to fill details such as active cable plug
> > > link training and cable rounded support.
> > > With USB4 cables, these VDO members need not be filled.
> > > 
> > > Suggested-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > Signed-off-by: Utkarsh Patel <utkarsh.h.patel@...el.com>
> > > 
> > > --
> > > Changes in v3:
> > > - Changed the commit mesage to reflect why TBT3 VDO is being used.
> > > - Added more details in the header file about the usage of TBT3 VDO.
> > > 
> > > Changes in v2:
> > > - No change.
> > > --
> > > ---
> > >  include/linux/usb/typec.h | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/include/linux/usb/typec.h b/include/linux/usb/typec.h
> > > index 6be558045942..25731ed863fa 100644
> > > --- a/include/linux/usb/typec.h
> > > +++ b/include/linux/usb/typec.h
> > > @@ -75,6 +75,10 @@ enum typec_orientation {
> > >  /*
> > >   * struct enter_usb_data - Enter_USB Message details
> > >   * @eudo: Enter_USB Data Object
> > > + * @tbt_cable_vdo: TBT3 Cable Discover Mode Response
> > 
> > This is fine..
> > 
> > > + * @tbt_cable_vdo needs to be filled with details of active cable plug link
> > > + * training and cable rounded support when thunderbolt 3 cable is being used to
> > > + * create USB4 connection. Do not fill this in case of USB4 cable.
> > 
> > But this is not. The description of the member tells what the member
> > contains, but it does not make sense to explain also how to use the
> > member in the same place.
> 
> Slightly tangential question here:
> 
> Is there a need to mention "active cable plug link training" and "cable
> rounded support" at all? Wouldn't it be sufficient to omit those in the
> description (in case some mux implementation wants to use the other fields
> of the VDO) ?

No, I don't think so. I think it would be enough to just mention that
we need the TBT3 Cable VDO only when the USB4 connection is created
using TBT3 cables. And that's it.


Br,

-- 
heikki