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When the Qualcomm pinctrl driver wants to Ack an interrupt, it does a read-modify-write on the interrupt status register. On some SoCs it makes sure that the status bit is 1 to "Ack" and on others it makes sure that the bit is 0 to "Ack". Presumably the first type of interrupt controller is a "write 1 to clear" type register and the second just let you directly set the interrupt status register. As far as I can tell from scanning structure definitions, the interrupt status bit is always in a register by itself. Thus with both types of interrupt controllers it is safe to "Ack" interrupts without doing a read-modify-write. We can do a simple write. It should be noted that if the interrupt status bit _was_ ever in a register with other things (like maybe status bits for other GPIOs): a) For "write 1 clear" type controllers then read-modify-write would be totally wrong because we'd accidentally end up clearing interrupts we weren't looking at. b) For "direct set" type controllers then read-modify-write would also be wrong because someone setting one of the other bits in the register might accidentally clear (or set) our interrupt. I say this simply to show that the current read-modify-write doesn't provide any sort of "future proofing" of the code. In fact (for "write 1 clear" controllers) the new code is slightly more "future proof" since it would allow more than one interrupt status bits to share a register. NOTE: this code fixes no bugs--it simply avoids an extra register read. Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Maulik Shah <mkshah@codeaurora.org> Tested-by: Maulik Shah <mkshah@codeaurora.org> Reviewed-by: Stephen Boyd <swboyd@chromium.org> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org> Link: https://lore.kernel.org/r/20210114191601.v7.2.I3635de080604e1feda770591c5563bd6e63dd39d@changeid 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.