linux-kernel - Re: [RFC PATCH v3 1/2] usb: typec: USB Type-C Port Manager (tcpm)

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Date:   Thu, 29 Sep 2016 09:36:37 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Jun Li <jun.li@....com>
Cc:     Guenter Roeck <groeck@...omium.org>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Chandra Sekhar Anagani <chandra.sekhar.anagani@...el.com>,
        Bruce Ashfield <bruce.ashfield@...driver.com>,
        Bin Gao <bin.gao@...el.com>,
        Pranav Tipnis <pranav.tipnis@...el.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [RFC PATCH v3 1/2] usb: typec: USB Type-C Port Manager (tcpm)

On Thu, Sep 29, 2016 at 7:35 AM, Jun Li <jun.li@....com> wrote:
> Hi Guenter,
>
>> -----Original Message-----
>> From: linux-usb-owner@...r.kernel.org [mailto:linux-usb-
>> owner@...r.kernel.org] On Behalf Of Guenter Roeck
>> Sent: Wednesday, August 24, 2016 5:11 AM
>> To: Felipe Balbi <felipe.balbi@...ux.intel.com>
>> Cc: Chandra Sekhar Anagani <chandra.sekhar.anagani@...el.com>; Bruce
>> Ashfield <bruce.ashfield@...driver.com>; Bin Gao <bin.gao@...el.com>;
>> Pranav Tipnis <pranav.tipnis@...el.com>; Heikki Krogerus
>> <heikki.krogerus@...ux.intel.com>; linux-kernel@...r.kernel.org; linux-
>> usb@...r.kernel.org; Guenter Roeck <groeck@...omium.org>
>> Subject: [RFC PATCH v3 1/2] usb: typec: USB Type-C Port Manager (tcpm)
>>
>> This driver implements the USB Type-C Power Delivery state machine
>> for both source and sink ports. Alternate mode support is not
>> fully implemented.
>>
>> The driver attaches to the USB Type-C class code implemented in
>> the following patches.
>>
>>       usb: typec: add driver for Intel Whiskey Cove PMIC USB Type-C PHY
>>       usb: USB Type-C connector class
>>
>> This driver only implements the state machine. Lower level drivers are
>> responsible for
>> - Reporting VBUS status and activating VBUS
>> - Setting CC lines and providing CC line status
>> - Setting line polarity
>> - Activating and deactivating VCONN
>> - Setting the current limit
>> - Activating and deactivating PD message transfers
>> - Sending and receiving PD messages
>>
>> The driver provides both a functional API as well as callbacks for
>> lower level drivers.
>>
>> Signed-off-by: Guenter Roeck <groeck@...omium.org>
>> ---
>> v3:
>> - Improve TCPM state machine resiliency if there are spurious CC line
>> changes
>>   while the state machine is in a transient change (waiting for a timeout)
>> - Update current limit after CC voltage level changes on a port which is
>> not
>>   PD capable.
>>
>> v2:
>> - Only update polarity if setting it was successful
>>   If setting the CC line polarity in the driver was not successful,
>>   don't update the internal polarity state.
>> - All PD messages are little endian; convert to and from CPU endianness.
>> - Avoid comparisons against NULL.
>> - Use u8/u16/u32 instead of uint8_t/uint16_t/uint32_t consistently.
>> - Callbacks into tcpm need to be lockless to avoid timing problems
>>   in low level drivers.
>> - Simplify callbacks; tcpm can request the current state of cc/vbus
>>   when it is ready to use it.
>>
>>  drivers/usb/typec/Kconfig  |    7 +
>>  drivers/usb/typec/Makefile |    1 +
>>  drivers/usb/typec/tcpm.c   | 3163
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  drivers/usb/typec/tcpm.h   |  137 ++
>>  include/linux/usb/pd.h     |  282 ++++
>>  include/linux/usb/pd_bdo.h |   31 +
>>  include/linux/usb/pd_vdo.h |  412 ++++++
>>  7 files changed, 4033 insertions(+)
>>  create mode 100644 drivers/usb/typec/tcpm.c
>>  create mode 100644 drivers/usb/typec/tcpm.h
>>  create mode 100644 include/linux/usb/pd.h
>>  create mode 100644 include/linux/usb/pd_bdo.h
>>  create mode 100644 include/linux/usb/pd_vdo.h
>>
>
> ...
>
>> +
>> +static void run_state_machine(struct tcpm_port *port)
>> +{
>> +     int ret;
>> +
>> +     port->enter_state = port->state;
>> +     switch (port->state) {
>> +     /* SRC states */
>> +     case SRC_UNATTACHED:
>> +             tcpm_swap_complete(port, -ENOTCONN);
>> +             tcpm_src_detach(port);
>> +             tcpm_set_cc(port, TYPEC_CC_RP_DEF);
>> +             if (port->typec_caps.type == TYPEC_PORT_DRP)
>> +                     tcpm_set_state(port, SNK_UNATTACHED, PD_T_DRP_SNK);
>
> With this and below, after disconnect, the DRP port state machine will be
> in infinite loop of state transition between SRC_UNATTACHED <--> SNK_UNATTACHED,
> correct?
>

Only while disconnected. It tries to alternatively connect as source
and as sink (being configured as DRP). Once a CC line state change is
reported it will transition out. I have a newer version of the patch
(not yet published) which supports DRP toggling by the TCPC. With that
enabled, TCPM does not change states until a CC state change is
reported.

Guenter

> Li Jun
> ...
>
>> +     /* SNK states */
>> +     case SNK_UNATTACHED:
>> +             tcpm_swap_complete(port, -ENOTCONN);
>> +             tcpm_snk_detach(port);
>> +             tcpm_set_cc(port, TYPEC_CC_RD);
>> +             if (port->typec_caps.type == TYPEC_PORT_DRP)
>> +                     tcpm_set_state(port, SRC_UNATTACHED, PD_T_DRP_SRC);
>> +             break;
>>