linux-kernel - Re: [PATCH] usb: typec: tcpm: always rediscover when swapping DR

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Date:   Tue, 17 Aug 2021 08:13:28 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Icenowy Zheng <icenowy@...c.io>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: tcpm: always rediscover when swapping DR

On 8/17/21 2:36 AM, Heikki Krogerus wrote:
> On Fri, Aug 13, 2021 at 12:31:31PM +0800, Icenowy Zheng wrote:
>> Currently, TCPM code omits discover when swapping to gadget, and assume
>> that no altmodes are available when swapping from gadget. However, we do
>> send discover when we get attached as gadget -- this leads to modes to be
>> discovered twice when attached as gadget and then swap to host.
>>
>> Always re-send discover when swapping DR, regardless of what change is
>> being made; and because of this, the assumption that no altmodes are
>> registered with gadget role is broken, and altmodes de-registeration is
>> always needed now.
>>
>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
>> ---
>>   drivers/usb/typec/tcpm/tcpm.c | 9 ++++-----
>>   1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
>> index b9bb63d749ec..ab6d0d51ee1c 100644
>> --- a/drivers/usb/typec/tcpm/tcpm.c
>> +++ b/drivers/usb/typec/tcpm/tcpm.c
>> @@ -4495,15 +4495,14 @@ static void run_state_machine(struct tcpm_port *port)
>>   		tcpm_set_state(port, ready_state(port), 0);
>>   		break;
>>   	case DR_SWAP_CHANGE_DR:
>> -		if (port->data_role == TYPEC_HOST) {
>> -			tcpm_unregister_altmodes(port);
>> +		tcpm_unregister_altmodes(port);
>> +		if (port->data_role == TYPEC_HOST)
>>   			tcpm_set_roles(port, true, port->pwr_role,
>>   				       TYPEC_DEVICE);
>> -		} else {
>> +		else
>>   			tcpm_set_roles(port, true, port->pwr_role,
>>   				       TYPEC_HOST);
>> -			port->send_discover = true;
>> -		}
>> +		port->send_discover = true;
>>   		tcpm_ams_finish(port);
>>   		tcpm_set_state(port, ready_state(port), 0);
>>   		break;
> 
> Why is it necessary to do discovery with data role swap in general?
> 
> thanks,
> 

Additional question: There are two patches pending related to DR_SWAP
and discovery. Are they both needed, or do they both solve the same
problem ?

Thanks,
Guenter