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

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>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index d6e3cfd54848..63ceed246b6f 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -380,6 +380,12 @@ config GPIO_RCAR
 	help
 	  Say yes here to support GPIO on Renesas R-Car SoCs.
 
+config GPIO_REG
+	bool
+	help
+	  A 32-bit single register GPIO fixed in/out implementation.  This
+	  can be used to represent any register as a set of GPIO signals.
+
 config GPIO_SPEAR_SPICS
 	bool "ST SPEAr13xx SPI Chip Select as GPIO support"
 	depends on PLAT_SPEAR