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2cbf9f514e
[ Upstream commit 1e61f6ab08786d66a11cfc51e13d6f08a6b06c56 ]
This patch fixes a race condition communication error, which ends up in
PD hard resets when losing the race. Some systems, like the Radxa ROCK
5B are powered through USB-C without any backup power source and use a
FUSB302 chip to do the PD negotiation. This means it is quite important
to avoid hard resets, since that effectively kills the system's
power-supply.
I've found the following race condition while debugging unplanned power
loss during booting the board every now and then:
1. lots of TCPM/FUSB302/PD initialization stuff
2. TCPM ends up in SNK_WAIT_CAPABILITIES (tcpm_set_pd_rx is enabled here)
3. the remote PD source does not send anything, so TCPM does a SOFT RESET
4. TCPM ends up in SNK_WAIT_CAPABILITIES for the second time
(tcpm_set_pd_rx is enabled again, even though it is still on)
At this point I've seen broken CRC good messages being send by the
FUSB302 with a logic analyzer sniffing the CC lines. Also it looks like
messages are being lost and things generally going haywire with one of
the two sides doing a hard reset once a broken CRC good message was send
to the bus.
I think the system is running into a race condition, that the FIFOs are
being cleared and/or the automatic good CRC message generation flag is
being updated while a message is already arriving.
Let's avoid this by caching the PD RX enabled state, as we have already
processed anything in the FIFOs and are in a good state. As a side
effect that this also optimizes I2C bus usage :)
As far as I can tell the problem theoretically also exists when TCPM
enters SNK_WAIT_CAPABILITIES the first time, but I believe this is less
critical for the following reason:
On devices like the ROCK 5B, which are powered through a TCPM backed
USB-C port, the bootloader must have done some prior PD communication
(initial communication must happen within 5 seconds after plugging the
USB-C plug). This means the first time the kernel TCPM state machine
reaches SNK_WAIT_CAPABILITIES, the remote side is not sending messages
actively. On other devices a hard reset simply adds some extra delay and
things should be good afterwards.
Fixes:
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| README | ||
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.