feat(xteink): count guest ADC reads per channel

Host tooling needs to know when the guest has actually sampled a button,
since the firmware only polls the resistor ladder between e-ink refreshes.

hw/adc/esp32c3_adc.c

@@ -26,9 +26,11 @@ static uint64_t esp32c3_adc_read(void *opaque, hwaddr addr, unsigned size)
         return ADC_DONE;
     }
     if (addr == ADC_DATA1 || addr == ADC_DATA2) {
-        return s->channel < ESP32C3_ADC_CHANNELS
-                   ? MIN(qatomic_read(&s->input[s->channel]), ADC_MAX)
-                   : ADC_MAX;
+        if (s->channel >= ESP32C3_ADC_CHANNELS) {
+            return ADC_MAX;
+        }
+        qatomic_inc(&s->samples[s->channel]);
+        return MIN(qatomic_read(&s->input[s->channel]), ADC_MAX);
     }
     return s->regs[addr / 4];
 }
@@ -60,6 +62,7 @@ static void esp32c3_adc_reset_hold(Object *obj, ResetType type)
     memset(s->regs, 0, sizeof(s->regs));
     for (int i = 0; i < ESP32C3_ADC_CHANNELS; i++) {
         s->input[i] = ADC_MAX;
+        s->samples[i] = 0;
     }
     s->channel = 0;
 }
@@ -75,6 +78,8 @@ static void esp32c3_adc_init(Object *obj)
     for (int i = 0; i < ESP32C3_ADC_CHANNELS; i++) {
         object_property_add_uint32_ptr(obj, "adci[*]", &s->input[i],
                                        OBJ_PROP_FLAG_READWRITE);
+        object_property_add_uint32_ptr(obj, "adcsamples[*]", &s->samples[i],
+                                       OBJ_PROP_FLAG_READ);
     }
     esp32c3_adc_reset_hold(obj, RESET_TYPE_COLD);
 }

include/hw/adc/esp32c3_adc.h

@@ -13,5 +13,7 @@ struct ESP32C3AdcState {
     MemoryRegion iomem;
     uint32_t regs[ESP32C3_ADC_IO_SIZE / sizeof(uint32_t)];
     uint32_t input[ESP32C3_ADC_CHANNELS];
+    /* Sample counters let a host driver hold a button until the guest has actually read it. */
+    uint32_t samples[ESP32C3_ADC_CHANNELS];
     uint8_t channel;
 };