dm: Introduce device sequence numbering

In U-Boot it is pretty common to number devices from 0 and access them
on the command line using this numbering. While it may come to pass that
we will move away from this numbering, the possibility seems remote at
present.

Given that devices within a uclass will have an implied numbering, it
makes sense to build this into driver model as a core feature. The cost
is fairly small in terms of code and data space.

With each uclass having numbered devices we can ask for SPI port 0 or
serial port 1 and receive a single device.

Devices typically request a sequence number using aliases in the device
tree. These are resolved when the device is probed, to deal with conflicts.
Sequence numbers need not be sequential and holes are permitted.

At present there is no support for sequence numbers using static platform
data. It could easily be added to 'struct driver_info' if needed, but it
seems better to add features as we find a use for them, and the use of -1
to mean 'no sequence' makes the default value somewhat painful.

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

3 files changed, 83 insertions, 0 deletions

diff --git a/include/dm/device.h b/include/dm/device.h
index 46799795e4..6005e7eeb5 100644
--- a/include/dm/device.h
+++ b/include/dm/device.h
@@ -55,6 +55,8 @@ struct driver_info;
  * @child_head: List of children of this device
  * @sibling_node: Next device in list of all devices
  * @flags: Flags for this device DM_FLAG_...
+ * @req_seq: Requested sequence number for this device (-1 = any)
+ * @seq: Allocated sequence number for this device (-1 = none)
  */
 struct udevice {
 	struct driver *driver;
@@ -69,8 +71,13 @@ struct udevice {
 	struct list_head child_head;
 	struct list_head sibling_node;
 	uint32_t flags;
+	int req_seq;
+	int seq;
 };
 
+/* Maximum sequence number supported */
+#define DM_MAX_SEQ	999
+
 /* Returns the operations for a device */
 #define device_get_ops(dev)	(dev->driver->ops)
 
@@ -161,4 +168,26 @@ void *dev_get_platdata(struct udevice *dev);
  */
 void *dev_get_priv(struct udevice *dev);
 
+/**
+ * device_find_child_by_seq() - Find a child device based on a sequence
+ *
+ * This searches for a device with the given seq or req_seq.
+ *
+ * For seq, if an active device has this sequence it will be returned.
+ * If there is no such device then this will return -ENODEV.
+ *
+ * For req_seq, if a device (whether activated or not) has this req_seq
+ * value, that device will be returned. This is a strong indication that
+ * the device will receive that sequence when activated.
+ *
+ * @parent: Parent device
+ * @seq_or_req_seq: Sequence number to find (0=first)
+ * @find_req_seq: true to find req_seq, false to find seq
+ * @devp: Returns pointer to device (there is only one per for each seq).
+ * Set to NULL if none is found
+ * @return 0 if OK, -ve on error
+ */
+int device_find_child_by_seq(struct udevice *parent, int seq_or_req_seq,
+			     bool find_req_seq, struct udevice **devp);
+
 #endif
diff --git a/include/dm/uclass-internal.h b/include/dm/uclass-internal.h
index 1434db3eb4..f718f37aff 100644
--- a/include/dm/uclass-internal.h
+++ b/include/dm/uclass-internal.h
@@ -82,4 +82,27 @@ struct uclass *uclass_find(enum uclass_id key);
  */
 int uclass_destroy(struct uclass *uc);
 
+/**
+ * uclass_find_device_by_seq() - Find uclass device based on ID and sequence
+ *
+ * This searches for a device with the given seq or req_seq.
+ *
+ * For seq, if an active device has this sequence it will be returned.
+ * If there is no such device then this will return -ENODEV.
+ *
+ * For req_seq, if a device (whether activated or not) has this req_seq
+ * value, that device will be returned. This is a strong indication that
+ * the device will receive that sequence when activated.
+ *
+ * The device is NOT probed, it is merely returned.
+ *
+ * @id: ID to look up
+ * @seq_or_req_seq: Sequence number to find (0=first)
+ * @find_req_seq: true to find req_seq, false to find seq
+ * @devp: Returns pointer to device (there is only one per for each seq)
+ * @return 0 if OK, -ve on error
+ */
+int uclass_find_device_by_seq(enum uclass_id id, int seq_or_req_seq,
+			      bool find_req_seq, struct udevice **devp);
+
 #endif
diff --git a/include/dm/uclass.h b/include/dm/uclass.h
index afd9923fb3..48ae2420df 100644
--- a/include/dm/uclass.h
+++ b/include/dm/uclass.h
@@ -106,6 +106,22 @@ int uclass_get(enum uclass_id key, struct uclass **ucp);
 int uclass_get_device(enum uclass_id id, int index, struct udevice **devp);
 
 /**
+ * uclass_get_device_by_seq() - Get a uclass device based on an ID and sequence
+ *
+ * If an active device has this sequence it will be returned. If there is no
+ * such device then this will check for a device that is requesting this
+ * sequence.
+ *
+ * The device is probed to activate it ready for use.
+ *
+ * @id: ID to look up
+ * @seq: Sequence number to find (0=first)
+ * @devp: Returns pointer to device (there is only one for each seq)
+ * @return 0 if OK, -ve on error
+ */
+int uclass_get_device_by_seq(enum uclass_id id, int seq, struct udevice **devp);
+
+/**
  * uclass_first_device() - Get the first device in a uclass
  *
  * @id: Uclass ID to look up
@@ -124,6 +140,21 @@ int uclass_first_device(enum uclass_id id, struct udevice **devp);
 int uclass_next_device(struct udevice **devp);
 
 /**
+ * uclass_resolve_seq() - Resolve a device's sequence number
+ *
+ * On entry dev->seq is -1, and dev->req_seq may be -1 (to allocate a
+ * sequence number automatically, or >= 0 to select a particular number.
+ * If the requested sequence number is in use, then this device will
+ * be allocated another one.
+ *
+ * Note that the device's seq value is not changed by this function.
+ *
+ * @dev: Device for which to allocate sequence number
+ * @return sequence number allocated, or -ve on error
+ */
+int uclass_resolve_seq(struct udevice *dev);
+
+/**
  * uclass_foreach_dev() - Helper function to iteration through devices
  *
  * This creates a for() loop which works through the available devices in