bootstd: Add bootflow_iter_check_mmc() helper

Some bootflows might be able to only boot from MMC devices.

Add a helper function these bootflows can use.

Reviewed-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Reviewed-by: Julien Masson <jmasson@baylibre.com>
Reviewed-by: Guillaume La Roque <glaroque@baylibre.com>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/bootflow.c b/boot/bootflow.c
index 9aa3179..59d77d2 100644
--- a/boot/bootflow.c
+++ b/boot/bootflow.c
@@ -575,6 +575,18 @@
 	return -ENOTSUPP;
 }
 
+int bootflow_iter_check_mmc(const struct bootflow_iter *iter)
+{
+	const struct udevice *media = dev_get_parent(iter->dev);
+	enum uclass_id id = device_get_uclass_id(media);
+
+	log_debug("uclass %d: %s\n", id, uclass_get_name(id));
+	if (id == UCLASS_MMC)
+		return 0;
+
+	return -ENOTSUPP;
+}
+
 int bootflow_iter_check_sf(const struct bootflow_iter *iter)
 {
 	const struct udevice *media = dev_get_parent(iter->dev);
diff --git a/include/bootflow.h b/include/bootflow.h
index 6affc5e..4d2fc7b 100644
--- a/include/bootflow.h
+++ b/include/bootflow.h
@@ -409,6 +409,15 @@
 int bootflow_iter_check_blk(const struct bootflow_iter *iter);
 
 /**
+ * bootflow_iter_check_mmc() - Check that a bootflow uses a MMC device
+ *
+ * This checks the bootdev in the bootflow to make sure it uses a mmc device
+ *
+ * Return: 0 if OK, -ENOTSUPP if some other device is used (e.g. ethernet)
+ */
+int bootflow_iter_check_mmc(const struct bootflow_iter *iter);
+
+/**
  * bootflow_iter_check_sf() - Check that a bootflow uses SPI FLASH
  *
  * This checks the bootdev in the bootflow to make sure it uses SPI flash