Hi Prashant, Thank you for the review and feedback. > 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). No, not in the case of USB4. > > 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? Since we do not have these information available with USB4 cables, we can use them to check for TBT support and then set tbt_cable_vdo. > > Best regards, > > -Prashant Sincerely, Utkarsh Patel.
