usb: typec: tcpm: Correct the PPS out_volt calculation

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Jan 30, 2019 at 11:13:53AM +0800, Kyle Tso wrote:
> When Sink negotiates PPS, the voltage range of selected PPS APDO might
> not cover the previous voltage (out_volt). If the previous out_volt is
> lower than the new min_volt, the output voltage in RDO might be set to
> an invalid value. For instance, supposed that the previous voltage is
> 5V, and the new voltage range in the APDO is 7V-12V. Then the output
> voltage in the RDO should not be set to 5V which is lower than the
> possible min_volt 7V.
> 
> Fix this by choosing the maximal value between the previous voltage and
> the new min_volt first. And ensure that this value will not exceed the
> new max_volt. The new out_volt will fall within the new voltage range
> while being the closest value compared to the previous out_volt.
> 
> Signed-off-by: Kyle Tso <kyletso@google.com>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  drivers/usb/typec/tcpm/tcpm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index f1d3e54210df..8f2af348bda5 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -2297,7 +2297,8 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
>  					      pdo_pps_apdo_max_voltage(snk));
>  		port->pps_data.max_curr = min_pps_apdo_current(src, snk);
>  		port->pps_data.out_volt = min(port->pps_data.max_volt,
> -					      port->pps_data.out_volt);
> +					      max(port->pps_data.min_volt,
> +						  port->pps_data.out_volt));
>  		port->pps_data.op_curr = min(port->pps_data.max_curr,
>  					     port->pps_data.op_curr);
>  	}
> -- 
> 2.20.1.495.gaa96b0ce6b-goog
>