gpio: pca953x: Improve interrupt support

The GPIO drivers with latch interrupt support (typically types starting
with PCAL) have interrupt status registers to determine which particular
inputs have caused an interrupt. Unfortunately there is no atomic
operation to read these registers and clear the interrupt. Clearing the
interrupt is done by reading the input registers.

The code was reading the interrupt status registers, and then reading
the input registers. If an input changed between these two events it was
lost.

The solution in this patch is to revert to the non-latch version of
code, i.e. remembering the previous input status, and looking for the
changes. This system results in no more I2C transfers, so is no slower.
The latch property of the device still means interrupts will still be
noticed if the input changes back to its initial state.

Fixes: 44896be ("gpio: pca953x: add PCAL9535 interrupt support for Galileo Gen2")
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240606033102.2271916-1-mark.tomlinson@alliedtelesis.co.nz
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: Mark Tomlinson

drivers/gpio/gpio-pca953x.c

@@ -841,25 +841,6 @@ static bool pca953x_irq_pending(struct pca953x_chip *chip, unsigned long *pendin
 	DECLARE_BITMAP(trigger, MAX_LINE);
 	int ret;
 
-	if (chip->driver_data & PCA_PCAL) {
-		/* Read the current interrupt status from the device */
-		ret = pca953x_read_regs(chip, PCAL953X_INT_STAT, trigger);
-		if (ret)
-			return false;
-
-		/* Check latched inputs and clear interrupt status */
-		ret = pca953x_read_regs(chip, chip->regs->input, cur_stat);
-		if (ret)
-			return false;
-
-		/* Apply filter for rising/falling edge selection */
-		bitmap_replace(new_stat, chip->irq_trig_fall, chip->irq_trig_raise, cur_stat, gc->ngpio);
-
-		bitmap_and(pending, new_stat, trigger, gc->ngpio);
-
-		return !bitmap_empty(pending, gc->ngpio);
-	}
-
 	ret = pca953x_read_regs(chip, chip->regs->input, cur_stat);
 	if (ret)
 		return false;