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[ Upstream commitea8be08cc9] The 'spi_stm32 44004000.spi: Communication suspended' message means that when using PIO, the kernel did not read the FIFO fast enough and so the SPI controller paused the transfer. Currently, this is printed on every single such event, so if the kernel is busy and the controller is pausing the transfers often, the kernel will be all the more busy scrolling this message into the log buffer every few milliseconds. That is not helpful. Instead, rate-limit the message and print it every once in a while. It is not possible to use the default dev_warn_ratelimited(), because that is still too verbose, as it prints 10 lines (DEFAULT_RATELIMIT_BURST) every 5 seconds (DEFAULT_RATELIMIT_INTERVAL). The policy here is to print 1 line every 50 seconds (DEFAULT_RATELIMIT_INTERVAL * 10), because 1 line is more than enough and the cycles saved on printing are better left to the CPU to handle the SPI. However, dev_warn_once() is also not useful, as the user should be aware that this condition is possibly recurring or ongoing. Thus the custom rate-limit policy. Finally, turn the message from dev_warn() to dev_dbg(), since the system does not suffer any sort of malfunction if this message appears, it is just slowing down. This further reduces the printing into the log buffer and frees the CPU to do useful work. Fixes:dcbe0d84df("spi: add driver for STM32 SPI controller") Signed-off-by: Marek Vasut <marex@denx.de> Cc: Alexandre Torgue <alexandre.torgue@st.com> Cc: Amelie Delaunay <amelie.delaunay@st.com> Cc: Antonio Borneo <borneo.antonio@gmail.com> Cc: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20200905151913.117775-1-marex@denx.de Signed-off-by: Mark Brown <broonie@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.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.