[PATCH v5 2/8] gpio: regmap: Add quirk for aliased data registers

[Sander Vanheule <sander@svanheule.net>]

Some chips have the read-only input and write-only output data registers
aliased to the same offset. As a result it is not possible to perform
read-modify-writes on the output values, when a line is still configured
as input.

Add a quirk for aliased data registers, and document how the regmap
should be set up for correct operation.

Signed-off-by: Sander Vanheule <sander@svanheule.net>
---
 drivers/gpio/gpio-regmap.c  |  7 ++++++-
 include/linux/gpio/regmap.h | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-regmap.c b/drivers/gpio/gpio-regmap.c
index 134cedf151a7..3a3d0d9a945c 100644
--- a/drivers/gpio/gpio-regmap.c
+++ b/drivers/gpio/gpio-regmap.c
@@ -15,6 +15,7 @@ struct gpio_regmap {
 	struct device *parent;
 	struct regmap *regmap;
 	struct gpio_chip gpio_chip;
+	unsigned int quirks;
 
 	int reg_stride;
 	int ngpio_per_reg;
@@ -68,7 +69,10 @@ static int gpio_regmap_get(struct gpio_chip *chip, unsigned int offset)
 	if (ret)
 		return ret;
 
-	ret = regmap_read(gpio->regmap, reg, &val);
+	if (gpio->quirks & GPIO_REGMAP_QUIRK_ALIASED_DATA)
+		ret = regmap_read_bypassed(gpio->regmap, reg, &val);
+	else
+		ret = regmap_read(gpio->regmap, reg, &val);
 	if (ret)
 		return ret;
 
@@ -227,6 +231,7 @@ struct gpio_regmap *gpio_regmap_register(const struct gpio_regmap_config *config
 
 	gpio->parent = config->parent;
 	gpio->regmap = config->regmap;
+	gpio->quirks = config->quirks;
 	gpio->ngpio_per_reg = config->ngpio_per_reg;
 	gpio->reg_stride = config->reg_stride;
 	gpio->reg_mask_xlate = config->reg_mask_xlate;
diff --git a/include/linux/gpio/regmap.h b/include/linux/gpio/regmap.h
index 334dd928042b..b0751a10fa4a 100644
--- a/include/linux/gpio/regmap.h
+++ b/include/linux/gpio/regmap.h
@@ -12,6 +12,17 @@ struct regmap;
 #define GPIO_REGMAP_ADDR_ZERO ((unsigned int)(-1))
 #define GPIO_REGMAP_ADDR(addr) ((addr) ? : GPIO_REGMAP_ADDR_ZERO)
 
+enum gpio_regmap_quirk {
+	/*
+	 * For hardware where the (read-only) input and (write-only) output
+	 * registers are aliased to the same offset. In this case the register
+	 * must not be marked as volatile and a regcache must be used, to cache
+	 * the write-only output values. Register reads for the input values
+	 * will be performed by bypassing the cache.
+	 */
+	GPIO_REGMAP_QUIRK_ALIASED_DATA = BIT(0),
+};
+
 /**
  * struct gpio_regmap_config - Description of a generic regmap gpio_chip.
  * @parent:		The parent device
@@ -31,6 +42,7 @@ struct regmap;
  * @reg_stride:		(Optional) May be set if the registers (of the
  *			same type, dat, set, etc) are not consecutive.
  * @ngpio_per_reg:	Number of GPIOs per register
+ * @quirks:		Flags indicating GPIO chip hardware issues
  * @irq_domain:		(Optional) IRQ domain if the controller is
  *			interrupt-capable
  * @reg_mask_xlate:     (Optional) Translates base address and GPIO
@@ -73,6 +85,7 @@ struct gpio_regmap_config {
 	unsigned int reg_dir_out_base;
 	int reg_stride;
 	int ngpio_per_reg;
+	unsigned int quirks;
 	struct irq_domain *irq_domain;
 
 	int (*reg_mask_xlate)(struct gpio_regmap *gpio, unsigned int base,
-- 
2.31.1