Re: [PATCH 5/5] usb: typec: fusb302: Enable SOP' communication

[Sebastian Reichel <sebastian.reichel@collabora.com>]

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Hi,

On Tue, Nov 03, 2026 at 03:21:26PM +0400, Alexey Charkov wrote:
> Let TCPM discover e-marked cables through the FUSB302 and learn their
> current and speed ratings.
> 
> Receive SOP' only while sourcing VCONN with PD reception on. Only the
> VCONN Source talks to the cable plug, and acking the traffic between the
> partner and the plug would collide with their own GoodCRC.
> 
> Switch SOP' reception off before VCONN or PD reception goes off and on
> only once both are on. If that fails, log it instead of failing the
> switch TCPM asked for: SOP' reception left off only costs cable
> discovery, and left on with VCONN off makes the port ack the partner's
> traffic with the cable plug until PD reception goes off, which beats
> keeping VCONN or PD reception in a state TCPM did not request.
> 
> Tested on a FUSB302B as source with an e-marked 5A EPR cable. The
> datasheet documents the auto-GoodCRC header bits for SOP only, but the
> cable plug took the chip's acks to its SOP' replies without retrying.
> 
> Signed-off-by: Alexey Charkov <alchark@flipper.net>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Greetings,

-- Sebastian

>  drivers/usb/typec/tcpm/fusb302.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
> index 8b3a2e095ef8..10f2dabf3318 100644
> --- a/drivers/usb/typec/tcpm/fusb302.c
> +++ b/drivers/usb/typec/tcpm/fusb302.c
> @@ -725,6 +725,27 @@ static int tcpm_set_polarity(struct tcpc_dev *dev,
>  	return 0;
>  }
>  
> +/*
> + * Without VCONN from us, SOP' traffic is between the partner and the cable
> + * plug, and our GoodCRC would collide with theirs. So stop receiving SOP'
> + * before VCONN or PD reception goes off, and start only once both are on.
> + * Neither is worth failing the VCONN or PD reception switch over.
> + */
> +static void fusb302_pd_set_sop_prime(struct fusb302_chip *chip, bool on)
> +{
> +	int ret;
> +
> +	if (on)
> +		ret = fusb302_i2c_set_bits(chip, FUSB_REG_CONTROL1,
> +					   FUSB_REG_CONTROL1_ENSOP1);
> +	else
> +		ret = fusb302_i2c_clear_bits(chip, FUSB_REG_CONTROL1,
> +					     FUSB_REG_CONTROL1_ENSOP1);
> +	if (ret < 0)
> +		fusb302_log(chip, "cannot turn SOP' rx %s, ret=%d",
> +			    str_on_off(on), ret);
> +}
> +
>  static int tcpm_set_vconn(struct tcpc_dev *dev, bool on)
>  {
>  	struct fusb302_chip *chip = container_of(dev, struct fusb302_chip,
> @@ -743,6 +764,8 @@ static int tcpm_set_vconn(struct tcpc_dev *dev, bool on)
>  		switches0_data = (chip->cc_polarity == TYPEC_POLARITY_CC1) ?
>  				 FUSB_REG_SWITCHES0_VCONN_CC2 :
>  				 FUSB_REG_SWITCHES0_VCONN_CC1;
> +	} else {
> +		fusb302_pd_set_sop_prime(chip, false);
>  	}
>  	ret = fusb302_i2c_mask_write(chip, FUSB_REG_SWITCHES0,
>  				     switches0_mask, switches0_data);
> @@ -750,6 +773,9 @@ static int tcpm_set_vconn(struct tcpc_dev *dev, bool on)
>  		goto done;
>  	chip->vconn_on = on;
>  	fusb302_log(chip, "vconn := %s", str_on_off(on));
> +
> +	if (on && chip->pd_rx_on)
> +		fusb302_pd_set_sop_prime(chip, true);
>  done:
>  	mutex_unlock(&chip->lock);
>  
> @@ -848,6 +874,8 @@ static int tcpm_set_pd_rx(struct tcpc_dev *dev, bool on)
>  		goto done;
>  	}
>  
> +	if (!on)
> +		fusb302_pd_set_sop_prime(chip, false);
>  	ret = fusb302_pd_rx_flush(chip);
>  	if (ret < 0) {
>  		fusb302_log(chip, "cannot flush pd rx buffer, ret=%d", ret);
> @@ -873,6 +901,9 @@ static int tcpm_set_pd_rx(struct tcpc_dev *dev, bool on)
>  
>  	chip->pd_rx_on = on;
>  	fusb302_log(chip, "pd := %s", str_on_off(on));
> +
> +	if (on && chip->vconn_on)
> +		fusb302_pd_set_sop_prime(chip, true);
>  done:
>  	mutex_unlock(&chip->lock);
>  
> @@ -1136,6 +1167,11 @@ static void fusb302_bc_lvl_handler_work(struct work_struct *work)
>  	mutex_unlock(&chip->lock);
>  }
>  
> +static bool tcpm_cable_comm_capable(struct tcpc_dev *dev)
> +{
> +	return true;
> +}
> +
>  static void init_tcpc_dev(struct tcpc_dev *fusb302_tcpc_dev)
>  {
>  	fusb302_tcpc_dev->init = tcpm_init;
> @@ -1150,6 +1186,7 @@ static void init_tcpc_dev(struct tcpc_dev *fusb302_tcpc_dev)
>  	fusb302_tcpc_dev->set_roles = tcpm_set_roles;
>  	fusb302_tcpc_dev->start_toggling = tcpm_start_toggling;
>  	fusb302_tcpc_dev->pd_transmit = tcpm_pd_transmit;
> +	fusb302_tcpc_dev->cable_comm_capable = tcpm_cable_comm_capable;
>  }
>  
>  static const char * const cc_polarity_name[] = {
> 
> -- 
> 2.56.0
> 

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