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SubjectRe: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO selection
On Thu, Dec 06, 2018 at 11:02:27AM +0800, 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.
>

Maybe a graphical description would help ?

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>

Makes sense to me. I am a bit concerned that it might cause odd regressions,
though. Did you test it with a few adapters ?

With the expectation that you did,

Reviewed-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);
> }
> --
> 2.20.0.rc2.403.gdbc3b29805-goog
>

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