[U-Boot] [RFC PATCH 16/22] dm: Add a way to indicate a preferred device within a uclass

[Simon Glass]

Where there are serveral device options that can be chosen, often one is
preferred. This can normally be handled by aliases in the device tree.

However, when a device can be specified either with platform data or
with a device tree node, which one should dm use? This situation happens
with sandbox, where we want to use the device tree version if we have
a device tree, and fall back to the platform data version if not. We need
this to work because without a console U-Boot will not function.

The original approach was just to take the first device in the uclass and
use that, but this does not work because the ordering is unknown.

The preferred device can be specified with a DM_FLAG_PREFER flag or a
'dm,prefer' property in the device tree node.

It is possible that a better approach will come to light in the future, but
this gets around the problem as it currently stands.

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

 drivers/core/device.c        |  5 +++++
 drivers/core/uclass.c        | 15 ++++++++++++++-
 include/dm/device.h          |  3 +++
 include/dm/uclass-internal.h |  3 ++-
 include/dm/uclass.h          | 15 +++++++++++++++
 test/dm/test-fdt.c           | 14 ++++++++++++++
 test/dm/test.dts             |  1 +
 7 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/drivers/core/device.c b/drivers/core/device.c
index 2c2634e..6b2c8f9 100644
--- a/drivers/core/device.c
+++ b/drivers/core/device.c
@@ -10,6 +10,7 @@
  */
 
 #include <common.h>
+#include <fdtdec.h>
 #include <malloc.h>
 #include <dm/device.h>
 #include <dm/device-internal.h>
@@ -21,6 +22,8 @@
 #include <linux/err.h>
 #include <linux/list.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 /**
  * device_chld_unbind() - Unbind all device's children from the device
  *
@@ -95,6 +98,8 @@ int device_bind(struct device *parent, struct driver *drv, const char *name,
 	dev->parent = parent;
 	dev->driver = drv;
 	dev->uclass = uc;
+	if (fdtdec_get_bool(gd->fdt_blob, of_offset, "dm,prefer"))
+		dev->flags |= DM_FLAG_PREFER;
 	if (!dev->platdata && drv->platdata_auto_alloc_size)
 		dev->flags |= DM_FLAG_ALLOC_PDATA;
 
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index afb5fdc..d02ea5e 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -149,7 +149,8 @@ int uclass_find_device(enum uclass_id id, int index, struct device **devp)
 		return ret;
 
 	list_for_each_entry(dev, &uc->dev_head, uclass_node) {
-		if (!index--) {
+		if (index == -1 ? (dev->flags & DM_FLAG_PREFER) :
+				!index--) {
 			*devp = dev;
 			return 0;
 		}
@@ -177,6 +178,18 @@ int uclass_get_device(enum uclass_id id, int index, struct device **devp)
 	return 0;
 }
 
+int uclass_get_preferred_device(enum uclass_id id, struct device **devp)
+{
+	int err;
+
+	err = uclass_get_device(id, -1, devp);
+	if (!err || err != -ENODEV)
+		return err;
+
+	/* Nothing found, just pick the first device */
+	return uclass_get_device(id, 0, devp);
+}
+
 int uclass_first_device(enum uclass_id id, struct device **devp)
 {
 	struct uclass *uc;
diff --git a/include/dm/device.h b/include/dm/device.h
index 32650fd..d3c04ed 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -26,6 +26,9 @@ struct driver_info;
 /* DM should init this device prior to relocation */
 #define DM_FLAG_PRE_RELOC	(1 << 2)
 
+/* DM should prefer this driver when searching a uclass */
+#define DM_FLAG_PREFER		(1 << 3)
+
 /**
  * struct device - An instance of a driver
  *
diff --git a/include/dm/uclass-internal.h b/include/dm/uclass-internal.h
index cc65d52..79b4d9e 100644
--- a/include/dm/uclass-internal.h
+++ b/include/dm/uclass-internal.h
@@ -13,7 +13,8 @@
 /**
  * uclass_find_device() - Return n-th child of uclass
  * @id:		Id number of the uclass
- * @index:	Position of the child in uclass's list
+ * @index:	Position of the child in uclass's list. If -1 then the
+ *		device marked with DM_FLAG_PREFER is returned, if any
  * #devp:	Returns pointer to device, or NULL on error
  *
  * The device is not prepared for use - this is an internal function
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
index ac5c147..2ca87fc 100644
--- a/include/dm/uclass.h
+++ b/include/dm/uclass.h
@@ -106,6 +106,21 @@ int uclass_get(enum uclass_id key, struct uclass **ucp);
 int uclass_get_device(enum uclass_id id, int index, struct device **devp);
 
 /**
+ * uclass_get_preferred_device() - Get the preferred uclass device
+ *
+ * id: ID to look up
+ * @ucp: Returns pointer to device (there is only one per for each ID)
+ *
+ * This returns the device with the DM_FLAG_PREFER flag set, if any.
+ * Otherwise it returns the first device.
+ *
+ * The device is probed to activate it ready for use.
+ *
+ * @return 0 if OK, -ve on error
+ */
+int uclass_get_preferred_device(enum uclass_id id, struct device **devp);
+
+/**
  * uclass_first_device() - Get the first device in a uclass
  *
  * @id: Uclass ID to look up
diff --git a/test/dm/test-fdt.c b/test/dm/test-fdt.c
index d6f5bb8..5dce48e 100644
--- a/test/dm/test-fdt.c
+++ b/test/dm/test-fdt.c
@@ -160,3 +160,17 @@ static int dm_test_fdt_pre_reloc(struct dm_test_state *dms)
 	return 0;
 }
 DM_TEST(dm_test_fdt_pre_reloc, 0);
+
+/* Test that autoprobe finds all the expected devices */
+static int dm_test_prefer(struct dm_test_state *dms)
+{
+	struct device *dev;
+
+	ut_assertok(uclass_get_preferred_device(UCLASS_TEST_FDT, &dev));
+	ut_assert(dev);
+
+	ut_asserteq_str("b-test", dev->name);
+
+	return 0;
+}
+DM_TEST(dm_test_prefer, DM_TESTF_SCAN_PDATA | DM_TESTF_SCAN_FDT);
diff --git a/test/dm/test.dts b/test/dm/test.dts
index b2eaddd..c42d4e7 100644
--- a/test/dm/test.dts
+++ b/test/dm/test.dts
@@ -36,6 +36,7 @@
 		reg = <3>;
 		compatible = "denx,u-boot-fdt-test";
 		ping-add = <3>;
+		prefer;
 	};
 
 	some-bus {
-- 
1.9.1.423.g4596e3a