gpio: pca953x: enable latch only on edge-triggered inputs

The latched input feature of the pca953x GPIO controller is useful
when an input is configured to trigger interrupts on rising or
falling edges, because it allows retrieving which edge type caused
a given interrupt even if the pin state changes again before the
interrupt handler has a chance to run. But for level-triggered
interrupts, reading the latched input state can cause an active
interrupt condition to be missed, e.g. if an active-low signal (for
which an IRQ_TYPE_LEVEL_LOW interrupt has been configured) triggers
an interrupt when switching to the inactive state, but then becomes
active again before the interrupt handler has a chance to run: in
this case, if the interrupt handler reads the latched input state,
it will wrongly assume that the interrupt is not pending.
Fix the above issue by enabling the latch only on edge-triggered
inputs, instead of all interrupt-enabled inputs.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
Reviewed-by: Ian Ray <ian.ray@gehealthcare.com>
Reviewed-by: Martyn Welch <martyn.welch@collabora.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index b46927f550389a5eca50d41042416bd4da19a1a9..9e72439f6c9261ae73e8909c1c5691d6a9e69ee5 100644 (file)
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -854,10 +854,13 @@ static void pca953x_irq_bus_sync_unlock(struct irq_data *d)
        int level;
 
        if (chip->driver_data & PCA_PCAL) {
+               DECLARE_BITMAP(latched_inputs, MAX_LINE);
                guard(mutex)(&chip->i2c_lock);
 
-               /* Enable latch on interrupt-enabled inputs */
-               pca953x_write_regs(chip, PCAL953X_IN_LATCH, chip->irq_mask);
+               /* Enable latch on edge-triggered interrupt-enabled inputs */
+               bitmap_or(latched_inputs, chip->irq_trig_fall, chip->irq_trig_raise, gc->ngpio);
+               bitmap_and(latched_inputs, latched_inputs, chip->irq_mask, gc->ngpio);
+               pca953x_write_regs(chip, PCAL953X_IN_LATCH, latched_inputs);
 
                bitmap_complement(irq_mask, chip->irq_mask, gc->ngpio);