gpio: mmio: Fix up inverted direction registers

The bgpio_init() takes one of two arguments to specify a register
to set the direction of the GPIO line: either dirout that
indicates that a 1 in the bit in that register sets the
corresponding line to output, or dirin which indicates that
a 1 in the bit in that register sets the corresponding line to
input. Conversely setting the bit to 0 on these will turn the
line into input and output respectively. One of these can
be defined but not both.

This means that a platform that sets a bit to 1 for output
only defines dirout and a platform that sets a bit to 0 for
output only defines dirin. In short this defines the polarity
of the direction register.

Both can also be left as NULL meaning the GPIO chip is either
input only or output only.

Tomer Maimon discovered that for get/set chips (those where the
get and set registers are defined but no separate clear register,
and specifying BGPIOF_READ_OUTPUT_REG_SET so that we say we
want to read the output value from the SET register)
we are unconditionally reading the value from the SET register
when the direction bit is 1 and from the DAT register when the
direction bit is 0, not taking the direction bit polarity into
account.

It would be expected that when the direction bit is inverted
(dirin is defined but not dirout) we read the current value from
the DAT register when the bit is 1 and from the SET register
when the bit is 0.

Currently only some versions of ATH79, brcmstb, some versions of
CLP711x, GE, IOP and Loongson use the dirin mode (a 1 in the
register means input). They are unaffected because
BGPIOF_READ_OUTPUT_REG_SET is not set on any of them. (They
do not read back the SET register to figure out the output
value.) So this is no regression with current drivers.

However the behaviour is wrong and does not work with Tomer's
new driver where he needs to use the BGIOF_READ_OUTPUT_REG_SET.
This fixes the above issue by:

- Instead of defining separate functions for the inverted case,
  set up a flag in the gpio_chip that indicates that the
  direction is inverted.
- Remove the special inverted functions for setting
  input/output and getting the direction, rely on the flag
  instead.
- Respect this flag in bgpio_get_set() and
  bgpio_get_set_multiple()

Reported-by: Tomer Maimon <tmaimon77@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 5382b5183b7e..0ea328e71ec9 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -201,6 +201,8 @@ static inline struct gpio_irq_chip *to_gpio_irq_chip(struct irq_chip *chip)
  * @reg_set: output set register (out=high) for generic GPIO
  * @reg_clr: output clear register (out=low) for generic GPIO
  * @reg_dir: direction setting register for generic GPIO
+ * @bgpio_dir_inverted: indicates that the direction register is inverted
+ *	(gpiolib private state variable)
  * @bgpio_bits: number of register bits used for a generic GPIO i.e.
  *	<register width> * 8
  * @bgpio_lock: used to lock chip->bgpio_data. Also, this is needed to keep
@@ -267,6 +269,7 @@ struct gpio_chip {
 	void __iomem *reg_set;
 	void __iomem *reg_clr;
 	void __iomem *reg_dir;
+	bool bgpio_dir_inverted;
 	int bgpio_bits;
 	spinlock_t bgpio_lock;
 	unsigned long bgpio_data;