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

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Message-ID: <YRuDG78N2mB5w37p@kuha.fi.intel.com>
Date:   Tue, 17 Aug 2021 12:36:27 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        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 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,

-- 
heikki