hw: allwinner-i2c: Fix TWI_CNTR_INT_FLAG on SUN6i SoCs

TWI_CNTR_INT_FLAG is W1C(write 1 to clear and write 0 has non-effect)
register on SUN6i based SoCs, we should lower interrupt when the guest
set this bit.

The linux kernel will hang in irq handler(mv64xxx_i2c_intr) if no
device connected on the i2c bus, next is the trace log:

allwinner_i2c_write write   CNTR(0x0c): 0xc4 A_ACK BUS_EN INT_EN
allwinner_i2c_write write   CNTR(0x0c): 0xcc A_ACK INT_FLAG BUS_EN INT_EN
allwinner_i2c_read  read    CNTR(0x0c): 0xcc A_ACK INT_FLAG BUS_EN INT_EN
allwinner_i2c_read  read    STAT(0x10): 0x20 STAT_M_ADDR_WR_NACK
allwinner_i2c_write write   CNTR(0x0c): 0x54 A_ACK M_STP BUS_EN
allwinner_i2c_write write   CNTR(0x0c): 0x4c A_ACK INT_FLAG BUS_EN
allwinner_i2c_read  read    CNTR(0x0c): 0x4c A_ACK INT_FLAG BUS_EN
allwinner_i2c_read  read    STAT(0x10): 0xf8 STAT_IDLE
allwinner_i2c_write write   CNTR(0x0c): 0x54 A_ACK M_STP BUS_EN
allwinner_i2c_write write   CNTR(0x0c): 0x4c A_ACK INT_FLAG BUS_EN
allwinner_i2c_read  read    CNTR(0x0c): 0x4c A_ACK INT_FLAG BUS_EN
allwinner_i2c_read  read    STAT(0x10): 0xf8 STAT_IDLE
...

Fix it.

Signed-off-by: qianfan Zhao <qianfanguijin@163.com>
Reviewed-by: Strahinja Jankovic <strahinja.p.jankovic@gmail.com>
Tested-by: Strahinja Jankovic <strahinja.p.jankovic@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/i2c/allwinner-i2c.c

@@ -357,10 +357,16 @@ static void allwinner_i2c_write(void *opaque, hwaddr offset,
                 s->stat = STAT_FROM_STA(STAT_IDLE);
                 s->cntr &= ~TWI_CNTR_M_STP;
             }
-            if ((s->cntr & TWI_CNTR_INT_FLAG) == 0) {
-                /* Interrupt flag cleared */
+
+            if (!s->irq_clear_inverted && !(s->cntr & TWI_CNTR_INT_FLAG)) {
+                /* Write 0 to clear this flag */
+                qemu_irq_lower(s->irq);
+            } else if (s->irq_clear_inverted && (s->cntr & TWI_CNTR_INT_FLAG)) {
+                /* Write 1 to clear this flag */
+                s->cntr &= ~TWI_CNTR_INT_FLAG;
                 qemu_irq_lower(s->irq);
             }
+
             if ((s->cntr & TWI_CNTR_A_ACK) == 0) {
                 if (STAT_TO_STA(s->stat) == STAT_M_DATA_RX_ACK) {
                     s->stat = STAT_FROM_STA(STAT_M_DATA_RX_NACK);
@@ -451,9 +457,25 @@ static const TypeInfo allwinner_i2c_type_info = {
     .class_init = allwinner_i2c_class_init,
 };
 
+static void allwinner_i2c_sun6i_init(Object *obj)
+{
+    AWI2CState *s = AW_I2C(obj);
+
+    s->irq_clear_inverted = true;
+}
+
+static const TypeInfo allwinner_i2c_sun6i_type_info = {
+    .name = TYPE_AW_I2C_SUN6I,
+    .parent = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(AWI2CState),
+    .instance_init = allwinner_i2c_sun6i_init,
+    .class_init = allwinner_i2c_class_init,
+};
+
 static void allwinner_i2c_register_types(void)
 {
     type_register_static(&allwinner_i2c_type_info);
+    type_register_static(&allwinner_i2c_sun6i_type_info);
 }
 
 type_init(allwinner_i2c_register_types)

include/hw/i2c/allwinner-i2c.h

@@ -28,6 +28,10 @@
 #include "qom/object.h"
 
 #define TYPE_AW_I2C "allwinner.i2c"
+
+/** Allwinner I2C sun6i family and newer (A31, H2+, H3, etc) */
+#define TYPE_AW_I2C_SUN6I    TYPE_AW_I2C "-sun6i"
+
 OBJECT_DECLARE_SIMPLE_TYPE(AWI2CState, AW_I2C)
 
 #define AW_I2C_MEM_SIZE         0x24
@@ -50,6 +54,8 @@ struct AWI2CState {
     uint8_t srst;
     uint8_t efr;
     uint8_t lcr;
+
+    bool irq_clear_inverted;
 };
 
 #endif /* ALLWINNER_I2C_H */