linux-kernel - RE: [PATCH v3 2/4] platform/chrome: cros_ec_typec: Use Thunderbolt 3 cable discover mode VDO in USB4 mode

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Date:   Fri, 20 Nov 2020 02:32:24 +0000
From:   "Patel, Utkarsh H" <utkarsh.h.patel@...el.com>
To:     Prashant Malani <pmalani@...omium.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
        "enric.balletbo@...labora.com" <enric.balletbo@...labora.com>,
        "Mani, Rajmohan" <rajmohan.mani@...el.com>,
        "Shaikh, Azhar" <azhar.shaikh@...el.com>
Subject: RE: [PATCH v3 2/4] platform/chrome: cros_ec_typec: Use Thunderbolt 3
 cable discover mode VDO in USB4 mode

Hi Prashant,

> -----Original Message-----
> From: Prashant Malani <pmalani@...omium.org>
> Sent: Thursday, November 19, 2020 12:09 AM
> To: Patel, Utkarsh H <utkarsh.h.patel@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-usb@...r.kernel.org;
> heikki.krogerus@...ux.intel.com; enric.balletbo@...labora.com; Mani,
> Rajmohan <rajmohan.mani@...el.com>; Shaikh, Azhar
> <azhar.shaikh@...el.com>
> Subject: Re: [PATCH v3 2/4] platform/chrome: cros_ec_typec: Use Thunderbolt
> 3 cable discover mode VDO in USB4 mode
> 
> Hi Utkarsh,
> 
> On Wed, Nov 18, 2020 at 10:32:09PM -0800, Utkarsh Patel wrote:
> > Configure Thunderbolt 3 cable generation value by filling Thunderbolt
> > 3 cable discover mode VDO to support rounded Thunderbolt 3 cables.
> > While we are here use Thunderbolt 3 cable discover mode VDO to fill
> > active cable plug link training value.
> >
> > Suggested-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > Signed-off-by: Utkarsh Patel <utkarsh.h.patel@...el.com>
> >
> > --
> > Changes in v3:
> > - Added a check for cable's TBT support before filling TBT3 discover mode
> >   VDO.
> >
> > Changes in v2:
> > - No change.
> > --
> > ---
> >  drivers/platform/chrome/cros_ec_typec.c | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/platform/chrome/cros_ec_typec.c
> > b/drivers/platform/chrome/cros_ec_typec.c
> > index 8111ed1fc574..68b17ee1d1ae 100644
> > --- a/drivers/platform/chrome/cros_ec_typec.c
> > +++ b/drivers/platform/chrome/cros_ec_typec.c
> > @@ -514,8 +514,18 @@ static int cros_typec_enable_usb4(struct
> cros_typec_data *typec,
> >  	else if (pd_ctrl->control_flags & USB_PD_CTRL_ACTIVE_CABLE)
> >  		data.eudo |= EUDO_CABLE_TYPE_RE_TIMER <<
> EUDO_CABLE_TYPE_SHIFT;
> >
> > -	data.active_link_training = !!(pd_ctrl->control_flags &
> > -				       USB_PD_CTRL_ACTIVE_LINK_UNIDIR);
> > +	/*
> > +	 * Filling TBT3 Cable VDO when TBT3 cable is being used to establish
> > +	 * USB4 connection.
> > +	 */
> > +	if (pd_ctrl->cable_gen) {
> > +		data.tbt_cable_vdo = TBT_MODE;
> > +
> > +		if (pd_ctrl->control_flags &
> USB_PD_CTRL_ACTIVE_LINK_UNIDIR)
> > +			data.tbt_cable_vdo |= TBT_CABLE_LINK_TRAINING;
> > +
> > +		data.tbt_cable_vdo |= TBT_SET_CABLE_ROUNDED(pd_ctrl-
> >cable_gen);
> > +	}
> 
> I think the following would decouple Rounded Support and Active Cable Link
> Training?:

Any reason you would want to decouple them?
As for the TBT3 active cable to create USB4 connection, it needs have rounded data rates. 

> 
> 	struct typec_thunderbolt_data data = {}; ...
> 	if (pd_ctrl->control_flags & USB_PD_CTRL_ACTIVE_LINK_UNIDIR)
> 		data.tbt_cable_vdo |= TBT_CABLE_LINK_TRAINING;
> 
> 	data.tbt_cable_vdo |= TBT_SET_CABLE_ROUNDED(pd_ctrl-
> >cable_gen);
> 
> 	if (data.tbt_cable_vdo)
> 		data.tbt_cable_vdo |= TBT_MODE;
> 
> 
> Best regards,
> 
> -Prashant

Sincerely,
Utkarsh Patel.