esp: Handle CMD_BUSRESET by resetting the SCSI bus

Per investigation on the linked ticket, SunOS issues a SCSI bus reset
to the ESP as part of its boot sequence. If this ESP command doesn't
cause devices to assert sense flag UNIT ATTENTION, SunOS will consider
the CD-ROM device to be non-compliant with Common Command Set (CCS).
In this condition, the SunOS installer's early userspace doesn't set
the installation source location to sr0 and the miniroot copy fails.

Signed-off-by: John Millikin <john@john-millikin.com>
Suggested-by: Bill Paul <noisetube@gmail.com>
Buglink: https://gitlab.com/qemu-project/qemu/-/issues/1127
Message-Id: <20220817053846.699310-1-john@john-millikin.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/esp.c

@@ -939,6 +939,11 @@ static void esp_soft_reset(ESPState *s)
     esp_hard_reset(s);
 }
 
+static void esp_bus_reset(ESPState *s)
+{
+    qbus_reset_all(BUS(&s->bus));
+}
+
 static void parent_esp_reset(ESPState *s, int irq, int level)
 {
     if (level) {
@@ -1067,6 +1072,7 @@ void esp_reg_write(ESPState *s, uint32_t saddr, uint64_t val)
             break;
         case CMD_BUSRESET:
             trace_esp_mem_writeb_cmd_bus_reset(val);
+            esp_bus_reset(s);
             if (!(s->wregs[ESP_CFG1] & CFG1_RESREPT)) {
                 s->rregs[ESP_RINTR] |= INTR_RST;
                 esp_raise_irq(s);