linux-kernel - Re: [PATCH 1/1] usb: typec: tcpci: add functions to read the VBUS voltage

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Date:   Tue, 7 May 2019 18:59:36 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Angus Ainslie (Purism)" <angus@...ea.ca>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: typec: tcpci: add functions to read the VBUS
 voltage

On 5/7/19 5:40 PM, Angus Ainslie (Purism) wrote:
> Show an error when the VBUS voltage is out of range.
> 
> Signed-off-by: Angus Ainslie (Purism) <angus@...ea.ca>
> ---
>   drivers/usb/typec/tcpm/tcpci.c | 35 ++++++++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpci.c b/drivers/usb/typec/tcpm/tcpci.c
> index a5746657b190..223941e11ef3 100644
> --- a/drivers/usb/typec/tcpm/tcpci.c
> +++ b/drivers/usb/typec/tcpm/tcpci.c
> @@ -261,6 +261,26 @@ static int tcpci_set_pd_rx(struct tcpc_dev *tcpc, bool enable)
>   	return 0;
>   }
>   
> +static int tcpci_get_vbus_voltage(struct tcpc_dev *tcpc)
> +{
> +	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
> +	u16 vbus_reg;
> +	unsigned int vbus_voltage;
> +	int ret, scale;
> +
> +	ret = tcpci_read16(tcpci, TCPC_VBUS_VOLTAGE, &vbus_reg);
> +	if (ret < 0)
> +		return ret;
> +
> +	vbus_voltage = vbus_reg & 0x3f;
> +
> +	scale = (vbus_reg >> 10) & 3;
> +	if (scale == 3)
> +		return -EIO;
> +
> +	return (vbus_voltage << scale) * 25;
> +}
> +
>   static int tcpci_get_vbus(struct tcpc_dev *tcpc)
>   {
>   	struct tcpci *tcpci = tcpc_to_tcpci(tcpc);
> @@ -401,6 +421,7 @@ static int tcpci_init(struct tcpc_dev *tcpc)
>   irqreturn_t tcpci_irq(struct tcpci *tcpci)
>   {
>   	u16 status;
> +	int ret;
>   
>   	tcpci_read16(tcpci, TCPC_ALERT, &status);
>   
> @@ -474,6 +495,20 @@ irqreturn_t tcpci_irq(struct tcpci *tcpci)
>   		tcpci_write16(tcpci, TCPC_FAULT_STATUS, fault_status);
>   	}
>   
> +	if (status & (TCPC_ALERT_V_ALARM_LO | TCPC_ALERT_V_ALARM_HI)) {
> +		ret = tcpci_get_vbus_voltage(&tcpci->tcpc);
> +
Extra empty line.

> +		if (ret >= 0) {
> +			if (status & TCPC_ALERT_V_ALARM_LO)
> +				dev_err(tcpci->dev, "Low VBUS voltage %d mV\n",
> +						ret);
> +
> +			if (status & TCPC_ALERT_V_ALARM_HI)
> +				dev_err(tcpci->dev, "High VBUS voltage %d mV\n",
> +						ret);
> +		}

This doesn't report anything if reading the VBUS voltage
returns an error.

Also, per TCPCI specification, you probably want to check
POWER_CONTROL.VBUS_VOLTAGE Monitor to see if it is enabled
in the first place.

On a higher level, the driver doesn't currently set limits for low
and high voltage alarms, and it doesn't enable those alarms. As such,
I wonder if/how you can get those alerts. Can you clarify ?

Thanks,
Guenter

> +	}
> +
>   	return IRQ_HANDLED;
>   }
>   EXPORT_SYMBOL_GPL(tcpci_irq);
>