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dd885d90c0
Kvaser's PCIe cards uses the KCAN FPGA IP block which has dual 4K
buffers for incoming messages shared by all (currently up to eight)
channels. While the driver processes messages in one buffer, new
incoming messages are stored in the other and so on.
The design of KCAN is such that a buffer must be fully read and then
released. Releasing a buffer will make the FPGA switch buffers. If the
other buffer contains at least one incoming message the FPGA will also
instantly issue a new interrupt, if not the interrupt will be issued
after receiving the first new message.
With IRQx interrupts, it takes a little time for the interrupt to
happen, enough for any previous ISR call to do it's business and
return, but MSI interrupts are way faster so this time is reduced to
almost nothing.
So with MSI, releasing the buffer HAS to be the very last action of
the ISR before returning, otherwise the new interrupt might be
"masked" by the kernel because the previous ISR call hasn't returned.
And the interrupts are edge-triggered so we cannot loose one, or the
ping-pong reading process will stop.
This is why this patch modifies the driver to use a single write to
the SRB_CMD register before returning.
Signed-off-by: Martin Jocic <martin.jocic@kvaser.com>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://patch.msgid.link/20240830153113.2081440-1-martin.jocic@kvaser.com
Fixes: 26ad340e58 ("can: kvaser_pciefd: Add driver for Kvaser PCIEcan devices")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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.