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

From: Guenter Roeck
Date: Tue Aug 17 2021 - 11:13:36 EST

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@xxxxxxx>
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);
- 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,
- } else {
+ else
tcpm_set_roles(port, true, port->pwr_role,
- port->send_discover = true;
- }
+ port->send_discover = true;
tcpm_set_state(port, ready_state(port), 0);

Why is it necessary to do discovery with data role swap in general?


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 ?