Re: [PATCH v2 2/2] usb: typec: fusb302: add support of supported_pd_rev

[Guenter Roeck]

On 2/8/22 19:34, Potin Lai wrote:
> Guenter Roeck 於 2022/2/8 下午 11:22 寫道:
> > On 2/8/22 03:22, Potin Lai wrote:
> > > Add support for passing supported PD rev to TCPM.
> > > If "supported-pd-rev" property exist, then return supported_pd_rev as
> > > defined value in DTS, otherwise return PD_MAX_REV
> > >
> > > Example of DTS:
> > >
> > > fusb302: typec-portc@22 {
> > >      compatible = "fcs,fusb302";
> > >      reg = <0x22>;
> > >      ...
> > >      supported-pd-rev=<1>; // PD_REV20
> > >      ...
> > > };
> >
> > The new property needs to be documented. However, I am not entirely sure
> > I understand why it is needed. Wouldn't the supported PD revision
> > be a chip (fusb302) specific constant ? If so, why does it need a
> > devicetree property ? I think that needs some additional explanation.
> >
> > Thanks,
> > Guenter
>
> My initially intend was adding flexibility for developer to decided which PD revision
> they want to use for negotiation.

I may be missing something, but I don't think that "flexibility for developer
to decide which PD revision they want to use for negotiation" is entirely appropriate.
This should be a chip property, not something a developer should decide. As written,
the code does accept PC version 3 for FUSB302 by default, which seems odd and unusual.
If the chip supports PD version 3, why artificially limit it to earlier PD revisions ?

I think this requires a detailed description of the use case. Is fusb302 indeed not able
to support a specific version of the power delivery specification ? If yes,
what is the limitation, and why would it need to be configurable with a devicetree
property ?

Thanks,
Guenter

> I saw your reply in another patch,  I agree with you, it will be simple and consistent if
> move "supported-pd-rev" to tcpm fwnode as other capabilities.
>
> Just want to double confirm, is "usb-connector.yaml" right place to put documentation
> if adding "supported-pd-rev" in fwnode?
>
> Thanks,
> Potin
>
> > > Signed-off-by: Potin Lai <potin.lai@xxxxxxxxxxxx>
> > > ---
> > >   drivers/usb/typec/tcpm/fusb302.c | 20 ++++++++++++++++++++
> > >   1 file changed, 20 insertions(+)
> > >
> > > diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
> > > index 72f9001b0792..8cff92d58b96 100644
> > > --- a/drivers/usb/typec/tcpm/fusb302.c
> > > +++ b/drivers/usb/typec/tcpm/fusb302.c
> > > @@ -109,6 +109,9 @@ struct fusb302_chip {
> > >       enum typec_cc_status cc2;
> > >       u32 snk_pdo[PDO_MAX_OBJECTS];
> > >   +    /* supported pd rev */
> > > +    u32 supported_pd_rev;
> > > +
> > >   #ifdef CONFIG_DEBUG_FS
> > >       struct dentry *dentry;
> > >       /* lock for log buffer access */
> > > @@ -1056,6 +1059,13 @@ static int tcpm_pd_transmit(struct tcpc_dev *dev, enum tcpm_transmit_type type,
> > >       return ret;
> > >   }
> > >   +static u32 tcpm_supported_pd_rev(struct tcpc_dev *dev)
> > > +{
> > > +    struct fusb302_chip *chip = container_of(dev, struct fusb302_chip,
> > > +                         tcpc_dev);
> > > +    return chip->supported_pd_rev;
> > > +}
> > > +
> > >   static enum typec_cc_status fusb302_bc_lvl_to_cc(u8 bc_lvl)
> > >   {
> > >       if (bc_lvl == FUSB_REG_STATUS0_BC_LVL_1230_MAX)
> > > @@ -1129,6 +1139,7 @@ static void init_tcpc_dev(struct tcpc_dev *fusb302_tcpc_dev)
> > >       fusb302_tcpc_dev->set_roles = tcpm_set_roles;
> > >       fusb302_tcpc_dev->start_toggling = tcpm_start_toggling;
> > >       fusb302_tcpc_dev->pd_transmit = tcpm_pd_transmit;
> > > +    fusb302_tcpc_dev->supported_pd_rev = tcpm_supported_pd_rev;
> > >   }
> > >     static const char * const cc_polarity_name[] = {
> > > @@ -1683,6 +1694,7 @@ static int fusb302_probe(struct i2c_client *client,
> > >       struct fusb302_chip *chip;
> > >       struct i2c_adapter *adapter = client->adapter;
> > >       struct device *dev = &client->dev;
> > > +    struct device_node *np = dev->of_node;
> > >       const char *name;
> > >       int ret = 0;
> > >   @@ -1756,6 +1768,14 @@ static int fusb302_probe(struct i2c_client *client,
> > >           dev_err(dev, "cannot request IRQ for GPIO Int_N, ret=%d", ret);
> > >           goto tcpm_unregister_port;
> > >       }
> > > +
> > > +    if (of_property_read_u32(np, "supported-pd-rev",
> > > +                &chip->supported_pd_rev) < 0) {
> > > +        chip->supported_pd_rev = PD_MAX_REV;
> > > +    } else if (chip->supported_pd_rev > PD_MAX_REV) {
> > > +        chip->supported_pd_rev = PD_MAX_REV;
> > > +    }
> >
> > The else part is also checked in the tcpm code and thus seems
> > to be redundant.
> >
> > > +
> > >       enable_irq_wake(chip->gpio_int_n_irq);
> > >       i2c_set_clientdata(client, chip);