RE: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO selection

[Adam Thomson <Adam.Thomson.Opensource@diasemi.com>]

On 17 December 2018 12:45, Kyle Tso wrote:

> On Mon, Dec 17, 2018 at 8:23 PM Adam Thomson
> <Adam.Thomson.Opensource@diasemi.com> wrote:
> >
> > 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
> >
> 
> noted!
> Thanks for the correction. I will fix this in the next patch.
> 
> > > 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>
> > >
> > > ---
> > > 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) {
> >
> > 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.
> 
> Source:
> 3.3V - 11V, 3A (9V programmable)
> 3.3V - 16V, 3A (15V programmable)
> 
> Sink
> 5V - 9V, 3A
> 
> In this case, the Sink will select "3.3V - 11V, 3A (9V programmable)"
> because the
> "max_op_mv" when dealing with both Source Cap will be the same.
> 
> See line#2269, "max_op_mv" will be limited by "max_snk_mv" which is 9V.
> And in line#2273, "max_op_mv" (of the second src_cap) fails the check because
> "max_mv", which is equal to the "max_op_mv" of the previous src_cap, is the
> same as it.

Ok, yes I missed the re-calculation of src_mw on line 2270. Apologies.

> 
> 2267                             if (min_src_mv <= max_snk_mv &&
> 2268                                 max_src_mv >= min_snk_mv) {
> 2269                                     max_op_mv = min(max_src_mv,
> max_snk_mv);
> 2270                                     src_mw = (max_op_mv * src_ma) / 1000;
> 2271                                     /* Prefer higher voltages if
> available */
> 2272                                     if ((src_mw == max_mw &&
> 2273                                          max_op_mv > max_mv) ||
> 2274                                         src_mw > max_mw) {
> 2275                                             src_pdo = i;
> 2276                                             snk_pdo = j;
> 2277                                             max_mw = src_mw;
> 2278                                             max_mv = max_op_mv;
> 2279                                     }
> 2280                             }
> 
> >
> > >                                               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
> >