pinctrl: qcom: No need to read-modify-write the interrupt status

pinctrl: qcom: No need to read-modify-write the interrupt status

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>