On Tue, Nov 17, 2020 at 10:19 AM Prashant Malani <pmalani@xxxxxxxxxxxx> wrote: > > Hi Utkarsh, > > On Fri, Nov 13, 2020 at 12:25:01PM -0800, Utkarsh Patel wrote: > > Configure Thunderbolt3/USB4 cable generation value by filing Thunderbolt 3 > > cable discover mode VDO to support rounded and non-rounded Thunderbolt3/ > > USB4 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@xxxxxxxxxxxxxxx> > > Signed-off-by: Utkarsh Patel <utkarsh.h.patel@xxxxxxxxx> > > > > -- > > 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..b7416e82c3b3 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); > > + /* > > + * This driver does not have access to the identity information or > > + * capabilities of the cable, so we don't know is it a real USB4 or > > + * TBT3 cable. Therefore pretending that it's always TBT3 cable by > > + * filling the TBT3 Cable VDO. > > + */ > > + data.tbt_cable_vdo = TBT_MODE; > > Is it safe to be making this assumption unconditionally? It might work for > Intel Mux agent but is it guaranteed to be safe for any other future > mux implementation? In other words, what if a "true" USB4 cable is > connected which doesn't have the Thunderbolt SVID alt mode? I dug into this a bit more and can maybe articulate my concern better: Is there a situation where both of the following are true ? : - Cable type = EUDO_CABLE_TYPE_OPTICAL or EUDO_CABLE_TYPE_RE_TIMER - No TBT_CABLE_LINK_TRAINING or TBT_CABLE_ROUNDED_SUPPORT defined (both these are 0). If both the above are true, then in Patch 7/8, wouldn't we never hit the else condition (labeled "Active USB cable") and therefore not set the mode_data correctly? > > (Pre-fetching some alternatives in case the answer is no) > > You might want to check with the Cros EC team if you can repurpose a bit of > the "reserved" field for specifying whether the cable is TBT or not. > > Either that or see if there is a way to determine from the pd_ctrl->cable_speed > whether the cable is actually TBT or not. It seems link cable_gen and USB_PD_CTRL_ACTIVE_LINK_UNIDIR are reasonable proxies for whether the cable has TBT support, so perhaps we should only set tbt_cable_vdo = TBT_MODE if either of those are non-zero? WDYT? Best regards, -Prashant
