hw/ssi: Introduce a ssi_get_cs() helper

Simple routine to retrieve a DeviceState object on a SPI bus using its
CS index. It will be useful for the board to wire the CS lines.

Cc: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/ssi/ssi.c

@@ -27,6 +27,21 @@ struct SSIBus {
 #define TYPE_SSI_BUS "SSI"
 OBJECT_DECLARE_SIMPLE_TYPE(SSIBus, SSI_BUS)
 
+DeviceState *ssi_get_cs(SSIBus *bus, uint8_t cs_index)
+{
+    BusState *b = BUS(bus);
+    BusChild *kid;
+
+    QTAILQ_FOREACH(kid, &b->children, sibling) {
+        SSIPeripheral *kid_ssi = SSI_PERIPHERAL(kid->child);
+        if (kid_ssi->cs_index == cs_index) {
+            return kid->child;
+        }
+    }
+
+    return NULL;
+}
+
 static const TypeInfo ssi_bus_info = {
     .name = TYPE_SSI_BUS,
     .parent = TYPE_BUS,