sandbox: i2c: Support i2c emulation with of-platdata

At present the i2c emulators require access to the devicetree, which is
not possible (by design) with of-platdata.

Add a way for drivers to record the of-platdata index of their emulator,
so that we can still find the emulator.

This allows i2c emulation to work with of-platdata.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/i2c.h b/include/i2c.h
index 7ae0c42..c0fe94c 100644
--- a/include/i2c.h
+++ b/include/i2c.h
@@ -93,6 +93,8 @@
  *			   datasheet explains it's usage of this addressing
  *			   mode.
  * @emul: Emulator for this chip address (only used for emulation)
+ * @emul_idx: Emulator index, used for of-platdata and set by each i2c chip's
+ *	bind() method. This allows i2c_emul_find() to work with of-platdata.
  */
 struct dm_i2c_chip {
 	uint chip_addr;
@@ -102,6 +104,7 @@
 #ifdef CONFIG_SANDBOX
 	struct udevice *emul;
 	bool test_mode;
+	int emul_idx;
 #endif
 };
 
@@ -555,6 +558,18 @@
 int i2c_emul_find(struct udevice *dev, struct udevice **emulp);
 
 /**
+ * i2c_emul_set_idx() - Set the emulator index for an i2c sandbox device
+ *
+ * With of-platdata we cannot find the emulator using the device tree, so rely
+ * on the bind() method of each i2c driver calling this function to tell us
+ * the of-platdata idx of the emulator
+ *
+ * @dev: i2c device to set the emulator for
+ * @emul_idx: of-platdata index for that emulator
+ */
+void i2c_emul_set_idx(struct udevice *dev, int emul_idx);
+
+/**
  * i2c_emul_get_device() - Find the device being emulated
  *
  * Given an emulator this returns the associated device