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gpio: add generic single-register fixed-direction GPIO driver

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Add a simple, generic, single register fixed-direction GPIO driver.
This is able to support a single register with a mixture of inputs
and outputs.

This is different from gpio-mmio and gpio-74xx-mmio:
* gpio-mmio doesn't allow a fixed direction, it assumes there is always
  a direction register.
* gpio-74xx-mmio only supports all-in or all-out setups
* gpio-74xx-mmio is DT only, this needs to support legacy too
* they don't double-read when getting the GPIO value, as required by
  some implementations that this driver supports
* we need to always do 32-bit reads, which bgpio doesn't guarantee
* the current output state may not be readable from the hardware
  register - reading may reflect input status but not output status.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Russell King 2016-08-31 08:49:44 +01:00 • committed by Linus Walleij
commit 380639c7cc
4 changed files with 183 additions and 0 deletions
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