dm: Allow drivers to be marked 'before relocation'

Driver model currently only operates after relocation is complete. In this
state U-Boot typically has a small amount of memory available. In adding
support for driver model prior to relocation we must try to use as little
memory as possible.

In addition, on some machines the memory has not be inited and/or the CPU
is not running at full speed or the data cache is off. These can reduce
execution performance, so the less initialisation that is done before
relocation the better.

An immediately-obvious improvement is to only initialise drivers which are
actually going to be used before relocation. On many boards the only such
driver is a serial UART, so this provides a very large potential benefit.

Allow drivers to mark themselves as 'pre-reloc' which means that they will
be initialised prior to relocation. This can be done either with a driver
flag or with a 'dm,pre-reloc' device tree property.

To support this, the various dm scanning function now take a 'pre_reloc_only'
parameter which indicates that only drivers marked pre-reloc should be
bound.

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

3 files changed, 14 insertions, 9 deletions

diff --git a/drivers/core/device.c b/drivers/core/device.c
index c73c339d18..86b9ff8911 100644
--- a/drivers/core/device.c
+++ b/drivers/core/device.c
@@ -129,14 +129,16 @@ fail_bind:
 	return ret;
 }
 
-int device_bind_by_name(struct udevice *parent, const struct driver_info *info,
-			struct udevice **devp)
+int device_bind_by_name(struct udevice *parent, bool pre_reloc_only,
+			const struct driver_info *info, struct udevice **devp)
 {
 	struct driver *drv;
 
 	drv = lists_driver_lookup_name(info->name);
 	if (!drv)
 		return -ENOENT;
+	if (pre_reloc_only && !(drv->flags & DM_FLAG_PRE_RELOC))
+		return -EPERM;
 
 	return device_bind(parent, drv, info->name, (void *)info->platdata,
 			   -1, devp);
diff --git a/drivers/core/lists.c b/drivers/core/lists.c
index 87164a5cf9..5f1c85fd6e 100644
--- a/drivers/core/lists.c
+++ b/drivers/core/lists.c
@@ -62,7 +62,7 @@ struct uclass_driver *lists_uclass_lookup(enum uclass_id id)
 	return NULL;
 }
 
-int lists_bind_drivers(struct udevice *parent)
+int lists_bind_drivers(struct udevice *parent, bool pre_reloc_only)
 {
 	struct driver_info *info =
 		ll_entry_start(struct driver_info, driver_info);
@@ -73,8 +73,8 @@ int lists_bind_drivers(struct udevice *parent)
 	int ret;
 
 	for (entry = info; entry != info + n_ents; entry++) {
-		ret = device_bind_by_name(parent, entry, &dev);
-		if (ret) {
+		ret = device_bind_by_name(parent, pre_reloc_only, entry, &dev);
+		if (ret && ret != -EPERM) {
 			dm_warn("No match for driver '%s'\n", entry->name);
 			if (!result || ret != -ENOENT)
 				result = ret;
diff --git a/drivers/core/root.c b/drivers/core/root.c
index 346d462470..ce4eef3054 100644
--- a/drivers/core/root.c
+++ b/drivers/core/root.c
@@ -46,7 +46,7 @@ int dm_init(void)
 	}
 	INIT_LIST_HEAD(&DM_UCLASS_ROOT_NON_CONST);
 
-	ret = device_bind_by_name(NULL, &root_info, &DM_ROOT_NON_CONST);
+	ret = device_bind_by_name(NULL, false, &root_info, &DM_ROOT_NON_CONST);
 	if (ret)
 		return ret;
 	ret = device_probe(DM_ROOT_NON_CONST);
@@ -64,11 +64,11 @@ int dm_uninit(void)
 	return 0;
 }
 
-int dm_scan_platdata(void)
+int dm_scan_platdata(bool pre_reloc_only)
 {
 	int ret;
 
-	ret = lists_bind_drivers(DM_ROOT_NON_CONST);
+	ret = lists_bind_drivers(DM_ROOT_NON_CONST, pre_reloc_only);
 	if (ret == -ENOENT) {
 		dm_warn("Some drivers were not found\n");
 		ret = 0;
@@ -80,7 +80,7 @@ int dm_scan_platdata(void)
 }
 
 #ifdef CONFIG_OF_CONTROL
-int dm_scan_fdt(const void *blob)
+int dm_scan_fdt(const void *blob, bool pre_reloc_only)
 {
 	int offset = 0;
 	int ret = 0, err;
@@ -89,6 +89,9 @@ int dm_scan_fdt(const void *blob)
 	do {
 		offset = fdt_next_node(blob, offset, &depth);
 		if (offset > 0 && depth == 1) {
+			if (pre_reloc_only &&
+			    !fdt_getprop(blob, offset, "u-boot,dm-pre-reloc", NULL))
+				continue;
 			err = lists_bind_fdt(gd->dm_root, blob, offset);
 			if (err && !ret)
 				ret = err;