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Date:   Tue, 17 Aug 2021 17:41:58 +0800
From:   Icenowy Zheng <icenowy@aosc.io>
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC:     Guenter Roeck <linux@roeck-us.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: typec: tcpm: always rediscover when swapping DR
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=E4=BA=8E 2021=E5=B9=B48=E6=9C=8817=E6=97=A5 GMT+08:00 =E4=B8=8B=E5=8D=885=
:36:27, Heikki Krogerus <heikki=2Ekrogerus@linux=2Eintel=2Ecom> =E5=86=99=
=E5=88=B0:
>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=2E 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=2E
>>=20
>> 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=2E
>>=20
>> Signed-off-by: Icenowy Zheng <icenowy@aosc=2Eio>
>> ---
>>  drivers/usb/typec/tcpm/tcpm=2Ec | 9 ++++-----
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>=20
>> diff --git a/drivers/usb/typec/tcpm/tcpm=2Ec b/drivers/usb/typec/tcpm/t=
cpm=2Ec
>> index b9bb63d749ec=2E=2Eab6d0d51ee1c 100644
>> --- a/drivers/usb/typec/tcpm/tcpm=2Ec
>> +++ b/drivers/usb/typec/tcpm/tcpm=2Ec
>> @@ -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 =3D=3D TYPEC_HOST) {
>> -			tcpm_unregister_altmodes(port);
>> +		tcpm_unregister_altmodes(port);
>> +		if (port->data_role =3D=3D 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 =3D true;
>> -		}
>> +		port->send_discover =3D 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?

I think it could be possible for devices to expose different altmode
with different role=2E

>
>thanks,
>