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The current driver does a read/modify/write of the output registers when changing a bit in __aspeed_gpio_set(). This is sub-optimal for a couple of reasons: - If any of the neighbouring GPIOs (sharing the shared register) isn't (yet) configured as an output, it will read the current input value, and then apply it to the output latch, which may not be what the user expects. There should be no bug in practice as aspeed_gpio_dir_out() will establish a new value but it's not great either. - The GPIO block in the aspeed chip is clocked rather slowly (typically 25Mhz). That extra MMIO read halves the maximum speed at which we can toggle the GPIO. This provides a significant performance improvement to the GPIO based FSI master. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Reviewed-by: Christopher Bostic <cbostic@linux.vnet.ibm.com> Reviewed-by: Andrew Jeffery <andrew@aj.id.au> Tested-by: Joel Stanley <joel@jms.id.au> Signed-off-by: Linus Walleij <linus.walleij@linaro.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.