PD 3.0 spec defines a new mechanism for power role swap called
Fast role swap. This change enables TCPM to support FRS when
acting as sink.
Once the explicit contract is negotiated, sink port is
expected to query the source port for sink caps to
determine whether the source is FRS capable.
Bits 23 & 24 of fixed pdo of the sink caps from the source, when
set, indicates the current needed by the source when fast role
swap is in progress(Implicit contract phasae). 0 indicates that
the source does not support Fast Role Swap.
Upon receiving the FRS signal from the source,
TCPC(TCPM_FRS_EVENT) informs TCPM to start the Fast role swap sequence.
1. TCPM sends FRS PD message: FR_SWAP_SEND
2. If response is not received within the expiry of
SenderResponseTimer, Error recovery is triggered.:
FR_SWAP_SEND_TIMEOUT
3. Upon receipt of the accept message, TCPM waits for
PSSourceOffTimer for PS_READY message from the partner:
FR_SWAP_SNK_SRC_NEW_SINK_READY.
TCPC is expected to autonomously turn on vbus once the FRS
signal is received and vbus voltage falls below vsafe5v within
tSrcFrSwap. This is different from traditional power role swap
where the vbus sourcing is turned on by TCPM.
4. By this time, TCPC most likely would have started to
source vbus, TCPM waits for tSrcFrSwap to see if the
lower level TCPC driver signals TCPM_SOURCING_VBUS event:
FR_SWAP_SNK_SRC_SOURCE_VBUS_APPLIED.
5. When TCPC signals sourcing vbus, TCPM sends PS_READY msg and
changes the CC pin from Rd to Rp. This is the end of fast
role swap sequence and TCPM initiates the sequnce to negotiate
explicit contract by transitioning into SRC_STARTUP after
SwapSrcStart.
The code is written based on the sequence described in "Figure 8-107:
Dual-role Port in Sink to Source Fast Role Swap State Diagram" of
USB Power Delivery Specification Revision 3.0, Version 1.2.
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20201008061556.1402293-7-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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