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If hub_activate() is called before D+ has stabilized after remote
wakeup, the following situation might occur:
__ ___________________
/ \ /
D+ __/ \__/
Hub _______________________________
| ^ ^ ^
| | | |
Host _____v__|___|___________|______
| | | |
| | | \-- Interrupt Transfer (*3)
| | \-- ClearPortFeature (*2)
| \-- GetPortStatus (*1)
\-- Host detects remote wakeup
- D+ goes high, Host starts running by remote wakeup
- D+ is not stable, goes low
- Host requests GetPortStatus at (*1) and gets the following hub status:
- Current Connect Status bit is 0
- Connect Status Change bit is 1
- D+ stabilizes, goes high
- Host requests ClearPortFeature and thus Connect Status Change bit is
cleared at (*2)
- After waiting 100 ms, Host starts the Interrupt Transfer at (*3)
- Since the Connect Status Change bit is 0, Hub returns NAK.
In this case, port_event() is not called in hub_event() and Host cannot
recognize device. To solve this issue, flag change_bits even if only
Connect Status Change bit is 1 when got in the first GetPortStatus.
This issue occurs rarely because it only if D+ changes during a very
short time between GetPortStatus and ClearPortFeature. However, it is
fatal if it occurs in embedded system.
Signed-off-by: Keiya Nobuta <nobuta.keiya@fujitsu.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20200109051448.28150-1-nobuta.keiya@fujitsu.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.