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The geni serial driver had the rather sketchy hack in it where it would adjust the number of bytes per RX FIFO word from 4 down to 1 if it detected that CONFIG_CONSOLE_POLL was enabled (for kgdb) and this was a console port (defined by the kernel directing output to this port via the "console=" command line argument). The problem with that sketchy hack is that it's possible to run kgdb over a serial port even if it isn't used for console. Let's avoid the hack by simply handling the 4-bytes-per-FIFO word case for kdb. We'll have to have a (very small) cache but that should be fine. A nice side effect of this patch is that an agetty (or similar) running on this port is less likely to drop characters. We'll have roughly 4 times the RX FIFO depth than we used to now. NOTE: the character cache here isn't shared between the polling API and the non-polling API. That means that, technically, the polling API could eat a few extra bytes. This doesn't seem to pose a huge problem in reality because we'll only get several characters per FIFO word if those characters are all received at nearly the same time and we don't really expect non-kgdb characters to be sent to the same port as kgdb at the exact same time we're exiting kgdb. ALSO NOTE: we still have the sketchy hack for setting the number of bytes per TX FIFO word in place, but that one is less bad. kgdb doesn't have any problem with this because it always just sends 1 byte at a time and waits for it to finish. The TX FIFO hack is only really needed for console output. In any case, a future patch will remove that hack, too. Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Evan Green <evgreen@chromium.org> Signed-off-by: Douglas Anderson <dianders@chromium.org> Link: https://lore.kernel.org/r/20200626125844.1.I8546ecb6c5beb054f70c5302d1a7293484212cd1@changeid Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org> |
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| README | ||
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.