1f3c85c22d
Right now, when a gpio value is set, the actual hardware pin gets set asynchronously. When linux write the output register, it takes some time until it is actually propagated to the output shift registers. If that output port is connected to an I2C mux for example, the linux driver assumes the I2C bus is already switched although it is not. Fortunately, there is a single shot mode with a feedback: you can trigger the single shot and the hardware will clear that bit once it has finished the clocking and strobed the load signal of the shift registers. This can take a considerable amount of time though. Measuremens have shown that it takes up to a whole burst cycle gap which is about 50ms on the largest setting. Therefore, we have to mark the output bank as sleepable. To avoid unnecessary waiting, just trigger the single shot if the value was actually changed. Signed-off-by: Michael Walle <michael@walle.cc> Link: https://lore.kernel.org/r/20220226204507.2511633-6-michael@walle.cc 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.
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.