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The event ring dequeue pointer field (ERDP) in xHC hardware is used to inform controller how far the driver has processed events on the event ring. In the case all events are handled and event ring is empty then the address of the TRB after the last processed one should be written. This TRB is both the enqueue and dequeue pointer. But in case we are writing the ERDP in the middle of processing several events then ERDP field should be written with the "up to and including" address of the last handled event TRB. Currenly each ERDP write by driver is done as if all events are handled and ring is empty. Fix this by adjusting the order when software dequeue "inc_deq()" is called and hardware dequeue "xhci_update_erst_dequeue()" is updated. Details in xhci 1.2 specification section 4.9.4: "System software shall write the Event Ring Dequeue Pointer (ERDP) register to inform the xHC that it has completed the processing of Event TRBs up to and including the Event TRB referenced by the ERDP. The detection of a Cycle bit mismatch in an Event TRB processed by software indicates the location of the xHC Event Ring Enqueue Pointer and that the Event Ring is empty. Software shall write the ERDP with the address of this TRB to indicate that it has processed all Events in the ring" This change depends on fixes made to relocate inc_deq() calls captured in the below commits: commit |
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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.