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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Message-ID: <20201119080906.GE3652649@google.com>
Date:   Thu, 19 Nov 2020 00:09:06 -0800
From:   Prashant Malani <pmalani@...omium.org>
To:     Utkarsh Patel <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,
        rajmohan.mani@...el.com, 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?:

	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