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Message-ID: <HE1PR1001MB1002719044E56D116949E2AE80BC0@HE1PR1001MB1002.EURPRD10.PROD.OUTLOOK.COM>
Date: Mon, 17 Dec 2018 12:23:32 +0000
From: Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To: Kyle Tso <kyletso@...gle.com>,
"linux@...ck-us.net" <linux@...ck-us.net>,
"heikki.krogerus@...ux.intel.com" <heikki.krogerus@...ux.intel.com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
Adam Thomson <Adam.Thomson.Opensource@...semi.com>
CC: "badhri@...gle.com" <badhri@...gle.com>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO
selection
On 17 December 2018 02:48, 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
relatively
> 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@...gle.com>
>
> ---
> Changelog since v1:
> - updated the commit message as suggested by Guenter Roeck <linux@...ck-
> 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) {
Sorry I didn't raise this before, but came to mind this morning when I was
considering your updates again. What happens if the Source validly provides two
PPS APDOs, for example:
3.3V - 11V, 3A (9V programmable)
3.3V - 16V, 3A (15V programmable)
and the sink APDO is:
5V - 9V, 3A
I think the code here will now select the higher range (15V programmable) as it
gives a larger power output value, even if the sink can only support a voltage
that's far smaller. I really don't think this is correct. *If* you are going to
allow selection of PPS APDOs that provide a larger voltage range than the Sink
can actually cope with, then I think you should at least select the lower of
those advertised which fulfils the needs of the Sink.
> 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);
> }
> --
> 2.20.0.405.gbc1bbc6f85-goog
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