hw/sd: add card-reparenting function

Provide a new function sdbus_reparent_card() in sd core for reparenting
a card from a SDBus to another one.

This function is required by the raspi platform, where the two SD
controllers can be dynamically switched.
Signed-off-by: NClement Deschamps <clement.deschamps@antfield.fr>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1488293711-14195-3-git-send-email-peter.maydell@linaro.org
Message-id: 20170224164021.9066-3-clement.deschamps@antfield.fr
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
[PMM: added a doc comment to the header file; changed to
 use new behaviour of qdev_set_parent_bus()]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/sd/core.c

@@ -131,6 +131,33 @@ void sdbus_set_readonly(SDBus *sdbus, bool readonly)
     }
 }
 
+void sdbus_reparent_card(SDBus *from, SDBus *to)
+{
+    SDState *card = get_card(from);
+    SDCardClass *sc;
+    bool readonly;
+
+    /* We directly reparent the card object rather than implementing this
+     * as a hotpluggable connection because we don't want to expose SD cards
+     * to users as being hotpluggable, and we can get away with it in this
+     * limited use case. This could perhaps be implemented more cleanly in
+     * future by adding support to the hotplug infrastructure for "device
+     * can be hotplugged only via code, not by user".
+     */
+
+    if (!card) {
+        return;
+    }
+
+    sc = SD_CARD_GET_CLASS(card);
+    readonly = sc->get_readonly(card);
+
+    sdbus_set_inserted(from, false);
+    qdev_set_parent_bus(DEVICE(card), &to->qbus);
+    sdbus_set_inserted(to, true);
+    sdbus_set_readonly(to, readonly);
+}
+
 static const TypeInfo sd_bus_info = {
     .name = TYPE_SD_BUS,
     .parent = TYPE_BUS,

include/hw/sd/sd.h

@@ -140,6 +140,17 @@ uint8_t sdbus_read_data(SDBus *sd);
 bool sdbus_data_ready(SDBus *sd);
 bool sdbus_get_inserted(SDBus *sd);
 bool sdbus_get_readonly(SDBus *sd);
+/**
+ * sdbus_reparent_card: Reparent an SD card from one controller to another
+ * @from: controller bus to remove card from
+ * @to: controller bus to move card to
+ *
+ * Reparent an SD card, effectively unplugging it from one controller
+ * and inserting it into another. This is useful for SoCs like the
+ * bcm2835 which have two SD controllers and connect a single SD card
+ * to them, selected by the guest reprogramming GPIO line routing.
+ */
+void sdbus_reparent_card(SDBus *from, SDBus *to);
 
 /* Functions to be used by SD devices to report back to qdevified controllers */
 void sdbus_set_inserted(SDBus *sd, bool inserted);