linux-kernel - Re: [PATCH 01/18] staging: typec: tcpm: Add get_usb2_current_limit tcpc

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Date:   Sun, 6 Aug 2017 07:52:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Hans de Goede <hdegoede@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Sebastian Reichel <sre@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, Liam Breck <liam@...workimprov.net>,
        Tony Lindgren <tony@...mide.com>, linux-pm@...r.kernel.org,
        devel@...verdev.osuosl.org
Subject: Re: [PATCH 01/18] staging: typec: tcpm: Add get_usb2_current_limit
 tcpc_dev callback

On 08/06/2017 07:29 AM, Hans de Goede wrote:
> Hi,
> 
> On 06-08-17 16:18, Guenter Roeck wrote:
>> On 08/06/2017 05:35 AM, Hans de Goede wrote:
>>> A Rp signalling the default current limit indicates that we're possibly
>>> connected to an USB2 power-source. In some cases the type-c
>>> port-controller may provide the capability to detect the current-limit
>>> for USB2 power-sources (through e.g. BC1.2 detection).
>>>
>>> This commit adds an optional get_usb2_current_limit tcpc_dev callback
>>> which allows the port-controller to return the detected current-limit
>>> if the CC pin is pulled up with Rp.
>>>
>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>>> ---
>>>   drivers/staging/typec/tcpm.c | 5 ++++-
>>>   drivers/staging/typec/tcpm.h | 1 +
>>>   2 files changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/staging/typec/tcpm.c b/drivers/staging/typec/tcpm.c
>>> index 20eb4ebcf8c3..9f5adace4309 100644
>>> --- a/drivers/staging/typec/tcpm.c
>>> +++ b/drivers/staging/typec/tcpm.c
>>> @@ -660,7 +660,10 @@ static u32 tcpm_get_current_limit(struct tcpm_port *port)
>>>           break;
>>>       case TYPEC_CC_RP_DEF:
>>>       default:
>>> -        limit = 0;
>>> +        if (port->tcpc->get_usb2_current_limit)
>>
>> I think this callback should just be get_current_limit.
> 
> This is only used in the Rp-def case, which usually indicates being connected
> with an A->C cable to a USB-2 device and the intend is for the callback to
> implement some USB-2 specific method to detect the supported current-limit,
> hence the name. If you prefer to name it just get_current_limit I can
> change it for v2, but IMHO the usb2 part of the name is important as this
> will not get called when USB-PD negotiation is used, nor when Rp has the Rp15
> or Rp30 values.
> 

As you say, it gets called in the Rp-def case, which can be set anytime.
I'd rather have a generic name and explain in tcpm.h as part of the API
description when it is used/called.

Note that it is also called in SNK_DISCOVERY if cc=Rp-def to calculate
and set the initial current limit, even with pd.

Thanks,
Guenter

> Regards,
> 
> Hans
> 
> 
> 
>>
>>> +            limit = port->tcpc->get_usb2_current_limit(port->tcpc);
>>> +        else
>>> +            limit = 0;
>>>           break;
>>>       }
>>> diff --git a/drivers/staging/typec/tcpm.h b/drivers/staging/typec/tcpm.h
>>> index 19c307d31a5a..01b7d89379a3 100644
>>> --- a/drivers/staging/typec/tcpm.h
>>> +++ b/drivers/staging/typec/tcpm.h
>>> @@ -108,6 +108,7 @@ struct tcpc_dev {
>>>       int (*init)(struct tcpc_dev *dev);
>>>       int (*get_vbus)(struct tcpc_dev *dev);
>>> +    int (*get_usb2_current_limit)(struct tcpc_dev *dev); /* Optional */
>>>       int (*set_cc)(struct tcpc_dev *dev, enum typec_cc_status cc);
>>>       int (*get_cc)(struct tcpc_dev *dev, enum typec_cc_status *cc1,
>>>                 enum typec_cc_status *cc2);
>>>
>>
>