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commit78ff751f8eupstream. A system bus error during a PDMA transfer can mess up the calculation of the transfer residual (the PDMA handshaking hardware lacks a byte counter). This results in data corruption. The algorithm in this patch anticipates a bus error by starting each transfer with a MOVE.B instruction. If a bus error is caught the transfer will be retried. If a bus error is caught later in the transfer (for a MOVE.W instruction) the transfer gets failed and subsequent requests for that target will use PIO instead of PDMA. This avoids the "!REQ and !ACK" error so the severity level of that message is reduced to KERN_DEBUG. Cc: Michael Schmitz <schmitzmic@gmail.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: stable@vger.kernel.org # v4.14+ Fixes:3a0f64bfa9("mac_scsi: Fix pseudo DMA implementation") Signed-off-by: Finn Thain <fthain@telegraphics.com.au> Reported-by: Chris Jones <chris@martin-jones.com> Tested-by: Stan Johnson <userm57@yahoo.com> Tested-by: Michael Schmitz <schmitzmic@gmail.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.