hw/sensor: Add IC_DEVICE_ID to ISL voltage regulators

This commit adds a passthrough for PMBUS_IC_DEVICE_ID to allow Renesas
voltage regulators to return the integrated circuit device ID if they
would like to.

The behavior is very device specific, so it hasn't been added to the
general PMBUS model. Additionally, if the device ID hasn't been set,
then the voltage regulator will respond with the error byte value.  The
guest error message will change slightly for IC_DEVICE_ID with this
commit.

Signed-off-by: Peter Delevoryas <pdel@fb.com>
Reviewed-by: Titus Rwantare <titusr@google.com>
Message-Id: <20220701000626.77395-3-me@pjd.dev>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/sensor/isl_pmbus_vr.c

@@ -15,6 +15,18 @@
 
 static uint8_t isl_pmbus_vr_read_byte(PMBusDevice *pmdev)
 {
+    ISLState *s = ISL69260(pmdev);
+
+    switch (pmdev->code) {
+    case PMBUS_IC_DEVICE_ID:
+        if (!s->ic_device_id_len) {
+            break;
+        }
+        pmbus_send(pmdev, s->ic_device_id, s->ic_device_id_len);
+        pmbus_idle(pmdev);
+        return 0;
+    }
+
     qemu_log_mask(LOG_GUEST_ERROR,
                   "%s: reading from unsupported register: 0x%02x\n",
                   __func__, pmdev->code);

include/hw/sensor/isl_pmbus_vr.h

@@ -12,12 +12,17 @@
 #include "hw/i2c/pmbus_device.h"
 #include "qom/object.h"
 
+#define TYPE_ISL69259   "isl69259"
 #define TYPE_ISL69260   "isl69260"
 #define TYPE_RAA228000  "raa228000"
 #define TYPE_RAA229004  "raa229004"
+#define ISL_MAX_IC_DEVICE_ID_LEN 16
 
 struct ISLState {
     PMBusDevice parent;
+
+    uint8_t ic_device_id[ISL_MAX_IC_DEVICE_ID_LEN];
+    uint8_t ic_device_id_len;
 };
 
 OBJECT_DECLARE_SIMPLE_TYPE(ISLState, ISL69260)