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Subject: Re: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO
 selection
To:     Kyle Tso <kyletso@google.com>, heikki.krogerus@linux.intel.com,
        gregkh@linuxfoundation.org, Adam.Thomson.Opensource@diasemi.com
Cc:     badhri@google.com, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20181217024805.122897-1-kyletso@google.com>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <3f116158-d900-1dcd-387f-d8129a0f0dd0@roeck-us.net>
Date:   Sun, 16 Dec 2018 18:57:11 -0800
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On 12/16/18 6:48 PM, Kyle Tso wrote:
> Current matching rules ensure that the voltage range of selected Source
> Capability is entirely within the range defined in one of the Sink
> Capabilities. This is reasonable but not practical because Sink may not
> support wide range of voltage when sinking power while Source could
> advertise its capabilities in raletively wider range. For example, a
> Source PDO advertising 3.3V-11V@3A (9V Prog of Fixed Nominal Voltage)
> will not be selected if the Sink requires 5V-12V@3A PPS power. However,
> the Sink could work well if the requested voltage range in RDOs is
> 5V-11V@3A.
> 
> Currently accepted:
> 		|--------- source -----|
> 	|----------- sink ---------------|
> 
> Currently not accepted:
> 			|--------- source -----|
> 	|----------- sink ---------------|
> 
> 	|--------- source -----|
> 		|----------- sink ---------------|
> 
> 	|--------- source -----------------|
> 		|------ sink -------|
> 
> To improve the usability, change the matching rules to what listed
> below:
> a. The Source PDO is selectable if any portion of the voltage range
>     overlaps one of the Sink PDO's voltage range.
> b. The maximum operational voltage will be the lower one between the
>     selected Source PDO and the matching Sink PDO.
> c. The maximum power will be the maximum operational voltage times the
>     maximum current defined in the selected Source PDO
> d. Select the Source PDO with the highest maximum power
> 
> Signed-off-by: Kyle Tso <kyletso@google.com>

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

> 
> ---
> Changelog since v1:
> - updated the commit message as suggested by Guenter Roeck <linux@roeck-us.net>
> ---
>   drivers/usb/typec/tcpm/tcpm.c | 29 +++++++++++++++++------------
>   1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 3620efee2688..3001df7bd602 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -2213,7 +2213,8 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
>   	unsigned int i, j, max_mw = 0, max_mv = 0;
>   	unsigned int min_src_mv, max_src_mv, src_ma, src_mw;
>   	unsigned int min_snk_mv, max_snk_mv;
> -	u32 pdo;
> +	unsigned int max_op_mv;
> +	u32 pdo, src, snk;
>   	unsigned int src_pdo = 0, snk_pdo = 0;
>   
>   	/*
> @@ -2263,16 +2264,18 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
>   					continue;
>   				}
>   
> -				if (max_src_mv <= max_snk_mv &&
> -				    min_src_mv >= min_snk_mv) {
> +				if (min_src_mv <= max_snk_mv &&
> +				    max_src_mv >= min_snk_mv) {
> +					max_op_mv = min(max_src_mv, max_snk_mv);
> +					src_mw = (max_op_mv * src_ma) / 1000;
>   					/* Prefer higher voltages if available */
>   					if ((src_mw == max_mw &&
> -					     min_src_mv > max_mv) ||
> +					     max_op_mv > max_mv) ||
>   					    src_mw > max_mw) {
>   						src_pdo = i;
>   						snk_pdo = j;
>   						max_mw = src_mw;
> -						max_mv = max_src_mv;
> +						max_mv = max_op_mv;
>   					}
>   				}
>   			}
> @@ -2285,14 +2288,16 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
>   	}
>   
>   	if (src_pdo) {
> -		pdo = port->source_caps[src_pdo];
> -
> -		port->pps_data.min_volt = pdo_pps_apdo_min_voltage(pdo);
> -		port->pps_data.max_volt = pdo_pps_apdo_max_voltage(pdo);
> -		port->pps_data.max_curr =
> -			min_pps_apdo_current(pdo, port->snk_pdo[snk_pdo]);
> +		src = port->source_caps[src_pdo];
> +		snk = port->snk_pdo[snk_pdo];
> +
> +		port->pps_data.min_volt = max(pdo_pps_apdo_min_voltage(src),
> +					      pdo_pps_apdo_min_voltage(snk));
> +		port->pps_data.max_volt = min(pdo_pps_apdo_max_voltage(src),
> +					      pdo_pps_apdo_max_voltage(snk));
> +		port->pps_data.max_curr = min_pps_apdo_current(src, snk);
>   		port->pps_data.out_volt =
> -			min(pdo_pps_apdo_max_voltage(pdo), port->pps_data.out_volt);
> +			min(port->pps_data.max_volt, port->pps_data.out_volt);
>   		port->pps_data.op_curr =
>   			min(port->pps_data.max_curr, port->pps_data.op_curr);
>   	}
>