Re: [PATCH v3] usb: typec: tcpci: don't touch CC line if it's Vconn source

[Guenter Roeck <linux@xxxxxxxxxxxx>]

On 1/13/22 1:29 AM, Xu Yang wrote:
> With the AMS and Collision Avoidance, tcpm often needs to change the CC's
> termination. When one CC line is sourcing Vconn, if we still change its
> termination, the voltage of the another CC line is likely to be fluctuant
> and unstable.
>
> Therefore, we should verify whether a CC line is sourcing Vconn before
> changing its termination and only change the termination that is not
> a Vconn line. This can be done by reading the Vconn Present bit of
> POWER_ STATUS register. To determine the polarity, we can read the
> Plug Orientation bit of TCPC_CONTROL register. Since Vconn can only be
> sourced if Plug Orientation is set.
>
> Fixes: 0908c5aca31e ("usb: typec: tcpm: AMS and Collision Avoidance")
> cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Xu Yang <xu.yang_2@xxxxxxx>

Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
> v2: changed subject line
> v3: optimized the commit message and code according to Guenter's suggestions
> ---
>   drivers/usb/typec/tcpm/tcpci.c | 26 ++++++++++++++++++++++++++
>   drivers/usb/typec/tcpm/tcpci.h |  1 +
>   2 files changed, 27 insertions(+)
>
> diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
> index 35a1307349a2..e07d26a3cd8e 100644
> --- a/drivers/usb/typec/tcpm/tcpci.c
> +++ b/drivers/usb/typec/tcpm/tcpci.c
> @@ -75,9 +75,25 @@ static int tcpci_write16(struct tcpci *tcpci, unsigned int reg, u16 val)
>   static int tcpci_set_cc(struct tcpc_dev *tcpc, enum typec_cc_status cc)
>   {
>   	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
> +	bool vconn_pres;
> +	enum typec_cc_polarity polarity = TYPEC_POLARITY_CC1;
>   	unsigned int reg;
>   	int ret;
>   
> +	ret = regmap_read(tcpci->regmap, TCPC_POWER_STATUS, &reg);
> +	if (ret < 0)
> +		return ret;
> +
> +	vconn_pres = !!(reg & TCPC_POWER_STATUS_VCONN_PRES);
> +	if (vconn_pres) {
> +		ret = regmap_read(tcpci->regmap, TCPC_TCPC_CTRL, &reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (reg & TCPC_TCPC_CTRL_ORIENTATION)
> +			polarity = TYPEC_POLARITY_CC2;
> +	}
> +
>   	switch (cc) {
>   	case TYPEC_CC_RA:
>   		reg = (TCPC_ROLE_CTRL_CC_RA << TCPC_ROLE_CTRL_CC1_SHIFT) |
> @@ -112,6 +128,16 @@ static int tcpci_set_cc(struct tcpc_dev *tcpc, enum typec_cc_status cc)
>   		break;
>   	}
>   
> +	if (vconn_pres) {
> +		if (polarity == TYPEC_POLARITY_CC2) {
> +			reg &= ~(TCPC_ROLE_CTRL_CC1_MASK << TCPC_ROLE_CTRL_CC1_SHIFT);
> +			reg |= (TCPC_ROLE_CTRL_CC_OPEN << TCPC_ROLE_CTRL_CC1_SHIFT);
> +		} else {
> +			reg &= ~(TCPC_ROLE_CTRL_CC2_MASK << TCPC_ROLE_CTRL_CC2_SHIFT);
> +			reg |= (TCPC_ROLE_CTRL_CC_OPEN << TCPC_ROLE_CTRL_CC2_SHIFT);
> +		}
> +	}
> +
>   	ret = regmap_write(tcpci->regmap, TCPC_ROLE_CTRL, reg);
>   	if (ret < 0)
>   		return ret;
> diff --git a/drivers/usb/typec/tcpm/tcpci.h b/drivers/usb/typec/tcpm/tcpci.h
> index 2be7a77d400e..b2edd45f13c6 100644
> --- a/drivers/usb/typec/tcpm/tcpci.h
> +++ b/drivers/usb/typec/tcpm/tcpci.h
> @@ -98,6 +98,7 @@
>   #define TCPC_POWER_STATUS_SOURCING_VBUS	BIT(4)
>   #define TCPC_POWER_STATUS_VBUS_DET	BIT(3)
>   #define TCPC_POWER_STATUS_VBUS_PRES	BIT(2)
> +#define TCPC_POWER_STATUS_VCONN_PRES	BIT(1)
>   #define TCPC_POWER_STATUS_SINKING_VBUS	BIT(0)
>   
>   #define TCPC_FAULT_STATUS		0x1f