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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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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.