[PATCH 1/3] hw/i2c/pmbus: Add idle state to return 0xff's

[Peter Delevoryas <me@pjd.dev>]

From: Peter Delevoryas <pdel@fb.com>

Signed-off-by: Peter Delevoryas <pdel@fb.com>
Reviewed-by: Titus Rwantare <titusr@google.com>
---
 hw/i2c/pmbus_device.c         | 9 +++++++++
 include/hw/i2c/pmbus_device.h | 7 +++++++
 2 files changed, 16 insertions(+)

diff --git a/hw/i2c/pmbus_device.c b/hw/i2c/pmbus_device.c
index 62885fa6a1..f89fea65f3 100644
--- a/hw/i2c/pmbus_device.c
+++ b/hw/i2c/pmbus_device.c
@@ -261,6 +261,11 @@ void pmbus_check_limits(PMBusDevice *pmdev)
     }
 }
 
+void pmbus_idle(PMBusDevice *pmdev)
+{
+    pmdev->code = PMBUS_IDLE_STATE;
+}
+
 /* assert the status_cml error upon receipt of malformed command */
 static void pmbus_cml_error(PMBusDevice *pmdev)
 {
@@ -984,6 +989,10 @@ static uint8_t pmbus_receive_byte(SMBusDevice *smd)
         }
         break;
 
+    case PMBUS_IDLE_STATE:
+        pmbus_send8(pmdev, PMBUS_ERR_BYTE);
+        break;
+
     case PMBUS_CLEAR_FAULTS:              /* Send Byte */
     case PMBUS_PAGE_PLUS_WRITE:           /* Block Write-only */
     case PMBUS_STORE_DEFAULT_ALL:         /* Send Byte */
diff --git a/include/hw/i2c/pmbus_device.h b/include/hw/i2c/pmbus_device.h
index 0f4d6b3fad..93f5d57c9d 100644
--- a/include/hw/i2c/pmbus_device.h
+++ b/include/hw/i2c/pmbus_device.h
@@ -155,6 +155,7 @@ enum pmbus_registers {
     PMBUS_MFR_MAX_TEMP_1            = 0xC0, /* R/W word */
     PMBUS_MFR_MAX_TEMP_2            = 0xC1, /* R/W word */
     PMBUS_MFR_MAX_TEMP_3            = 0xC2, /* R/W word */
+    PMBUS_IDLE_STATE                = 0xFF,
 };
 
 /* STATUS_WORD */
@@ -527,6 +528,12 @@ int pmbus_page_config(PMBusDevice *pmdev, uint8_t page_index, uint64_t flags);
  */
 void pmbus_check_limits(PMBusDevice *pmdev);
 
+/**
+ * Enter an idle state where only the PMBUS_ERR_BYTE will be returned
+ * indefinitely until a new command is issued.
+ */
+void pmbus_idle(PMBusDevice *pmdev);
+
 extern const VMStateDescription vmstate_pmbus_device;
 
 #define VMSTATE_PMBUS_DEVICE(_field, _state) {                       \
-- 
2.37.0