[PULL 40/83] hw/gpio: pca9552: apply input polarity inversion on read

From: Emmanuel Blot <[email protected]>

The PCA9535 polarity inversion register inverts the value read back from
the input port for every pin, regardless of its direction, and does not
affect the output drive or the physical pin level.

Store the raw pin level in the input register and apply the polarity
inversion when the input port is read, instead of XORing it into the
stored value of output-configured pins only. The interrupt output now
reflects the raw pin level, matching the datasheet.

Signed-off-by: Emmanuel Blot <[email protected]>
Reviewed-by: Glenn Miles <[email protected]>
Link: https://lore.kernel.org/qemu-devel/[email protected]
Signed-off-by: Cédric Le Goater <[email protected]>
---
 hw/gpio/pca9552.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/hw/gpio/pca9552.c b/hw/gpio/pca9552.c
index 66f699bf6a0b..24f646541582 100644
--- a/hw/gpio/pca9552.c
+++ b/hw/gpio/pca9552.c
@@ -167,9 +167,12 @@ static void pca955x_update_pin_input(PCA955xState *s)
             /* PCA9535: Simple GPIO behavior */
             uint8_t config_reg = PCA9535_CONFIG0 + (i / 8);
             uint8_t output_reg = PCA9535_OUTPUT0 + (i / 8);
-            uint8_t polarity_reg = PCA9535_POLARITY0 + (i / 8);
 
-            /* Check if pin is configured as input */
+            /*
+             * The input register holds the raw pin logic level; the
+             * polarity inversion register is only applied when the input
+             * port is read (see pca955x_read()).
+             */
             if (s->regs[config_reg] & bit_mask) {
                 /* Input mode - reflect external state */
                 if (s->ext_state[i] == PCA9552_PIN_LOW) {
@@ -179,12 +182,8 @@ static void pca955x_update_pin_input(PCA955xState *s)
                 }
             } else {
                 /* Output mode - reflect output register value */
-                uint8_t output_bit = s->regs[output_reg] & bit_mask;
-                uint8_t polarity_bit = s->regs[polarity_reg] & bit_mask;
-
-                /* Apply polarity inversion if set */
                 s->regs[input_reg] = (s->regs[input_reg] & ~bit_mask) |
-                                    ((output_bit ^ polarity_bit) & bit_mask);
+                                     (s->regs[output_reg] & bit_mask);
             }
         }
 
@@ -206,6 +205,18 @@ static uint8_t pca955x_read(PCA955xState *s, uint8_t reg)
         return 0xFF;
     }
 
+    /*
+     * On the GPIO variants, reading an input port returns the raw pin
+     * levels XORed with the polarity inversion register, as specified by
+     * the datasheet.
+     */
+    if (!k->has_led_support &&
+        (reg == PCA9535_INPUT0 || reg == PCA9535_INPUT1)) {
+        uint8_t polarity_reg = PCA9535_POLARITY0 + (reg - PCA9535_INPUT0);
+
+        return s->regs[reg] ^ s->regs[polarity_reg];
+    }
+
     return s->regs[reg];
 }
 
-- 
2.55.0