linux-kernel - Re: [PATCH] usb: typec: don't disable sink or source on initialization

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Date:   Sun, 09 Sep 2018 08:08:46 -0600
From:   Angus Ainslie <angus@...ea.ca>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Guenter Roeck <groeck7@...il.com>
Subject: Re: [PATCH] usb: typec: don't disable sink or source on  initialization

Hi Guenter

On 2018-09-07 06:55, Guenter Roeck wrote:
> On 09/07/2018 03:34 AM, Heikki Krogerus wrote:
>> +Guenter
>> 
>> On Thu, Sep 06, 2018 at 01:26:44PM -0600, Angus Ainslie (Purism) 
>> wrote:
>>> If the board is being powered by USB disabling the source and sink
>>> can remove power from the board. Default to source and sink enabled.
>>> 
> 
> Seems to me that might violate the specification, and cause trouble for 
> systems
> where vbus has to be off initially. It may be better to provide this 
> kind of
> information as configuration parameter instead of imposing it on 
> everyone.
> 

It felt like it would not be the correct thing to do either. I've tried 
re-arranging the code in tcpci.c to enable the sink before disabling the 
source but the only way I found to not disable the power was by setting 
both of those to true.

What about adding some device tree entries for the initial vbus state 
and default to false if they are not present ?

init-vbus-source and init-vbus-charge ?

Angus

> Guenter
> 
>>> Signed-off-by: Angus Ainslie (Purism) <angus@...ea.ca>
>>> ---
>>>   drivers/usb/typec/tcpm.c | 8 +++++---
>>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>> 
>>> diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
>>> index ca7bedb46f7f..a1b819cf31da 100644
>>> --- a/drivers/usb/typec/tcpm.c
>>> +++ b/drivers/usb/typec/tcpm.c
>>> @@ -2462,9 +2462,11 @@ static int tcpm_init_vbus(struct tcpm_port 
>>> *port)
>>>   {
>>>   	int ret;
>>>   -	ret = port->tcpc->set_vbus(port->tcpc, false, false);
>>> -	port->vbus_source = false;
>>> -	port->vbus_charge = false;
>>> +	/* default to source and sink enabled in case USB is our only power
>>> +	 * source */
> 
> I am personally in favor of standard multi-line comments.
> 
>>> +	ret = port->tcpc->set_vbus(port->tcpc, true, true);
>>> +	port->vbus_source = true;
>>> +	port->vbus_charge = true;
>>>   	return ret;
>>>   }
>>