gpio: aspeed: Add "Read Data" register to read the write latch

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The Aspeed GPIO hardware has a quirk: the value register, for an
output GPIO, doesn't contain the last value written (the write
latch content) but the sampled input value.

This means that when reading back shortly after writing, you can
get an incorrect value as the input value is delayed by a few
synchronizers.

The HW supports a separate read-only register "Data Read Register"
which allows you to read the write latch instead.

This adds the definition for it, and uses it for the initial
population of the GPIO value cache. It will be used more in
subsequent patches.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

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Benjamin Herrenschmidt 2018-06-29 14:11:17 +10:00 • committed by Linus Walleij

parent 44ddf559d5

commit c67dda88cc

1 changed files with 27 additions and 2 deletions

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drivers/gpio/gpio-aspeed.c

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