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EOI (End Or Identify) is a hardware line on the GPIB bus that can be
asserted with the last byte of a message to indicate the end of the
transfer to the receiving device.
In this driver, a write with send_eoi true is done in 3 parts:
Send first byte directly
Send remaining but 1 bytes using the fifo
Send the last byte directly with EOI asserted
The first byte in a write is always sent by writing to the tms9914
chip directly to setup for the subsequent fifo transfer. We were not
checking for a 1 byte write with send_eoi true resulting in EOI not
being asserted. Since the fifo transfer was not executed
(fifotransfersize == 0) the retval in the test after the fifo transfer
code was still 1 from the preceding direct write. This caused it to
return without executing the final direct write which would have sent
an unsollicited extra byte.
For a 2 byte message the first byte was sent directly. But since the
fifo transfer was not executed (fifotransfersize == 1) and the retval
in the test after the fifo transfer code was still 1 from the
preceding first byte write it returned before the final direct byte
write with send_eoi true. The second byte was then sent as a separate
1 byte write to complete the 2 byte write count again without EOI
being asserted as above.
Only send the first byte directly if more than 1 byte is to be
transferred with send_eoi true.
Also check for retval < 0 for the error return in case the fifo code
is not used (1 or 2 byte message with send_eoi true).
Fixes: 09a4655ee1 ("staging: gpib: Add HP/Agilent/Keysight 8235xx PCI GPIB driver")
Cc: stable <stable@kernel.org>
Tested-by: Dave Penkler <dpenkler@gmail.com>
Signed-off-by: Dave Penkler <dpenkler@gmail.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 reStructuredText 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.