[U-Boot] [PATCH v4 06/33] dm: Improve handling of a missing uclass

[Simon Glass]

When a uclass definition is missing, no drivers in that uclass can operate.
This can happen if a board has a strange collection of options (e.g. the
driver is enabled but the uclass is not).

Unfortunately this is very confusing at present. Starting up driver model
results in a -ENOENT error, which is pretty generic. Quite a big of digging
is needed to get to the root cause.

To help with this, change the error to a very strange one with no other
users in U-Boot. Also add a debug message.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

Changes in v4: None
Changes in v3: None
Changes in v2: None

 drivers/core/device.c | 4 +++-
 drivers/core/uclass.c | 7 ++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/core/device.c b/drivers/core/device.c
index 4f060ee..eefd1cb 100644
--- a/drivers/core/device.c
+++ b/drivers/core/device.c
@@ -39,8 +39,10 @@ int device_bind(struct udevice *parent, const struct driver *drv,
 		return -EINVAL;
 
 	ret = uclass_get(drv->id, &uc);
-	if (ret)
+	if (ret) {
+		debug("Missing uclass for driver %s\n", drv->name);
 		return ret;
+	}
 
 	dev = calloc(1, sizeof(struct udevice));
 	if (!dev)
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index f63ff59..e800c28 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -58,7 +58,12 @@ static int uclass_add(enum uclass_id id, struct uclass **ucp)
 	if (!uc_drv) {
 		debug("Cannot find uclass for id %d: please add the UCLASS_DRIVER() declaration for this UCLASS_... id\n",
 		      id);
-		return -ENOENT;
+		/*
+		 * Use a strange error to make this case easier to find. When
+		 * a uclass is not available it can prevent driver model from
+		 * starting up and this failure is otherwise hard to debug.
+		 */
+		return -EPFNOSUPPORT;
 	}
 	uc = calloc(1, sizeof(*uc));
 	if (!uc)
-- 
2.5.0.457.gab17608