[dt] Add basic concept of a devicetree bus

Add a basic model for devices instantiated by parsing the system
flattened device tree, with drivers matched via the "compatible"
property for any non-root node.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/bus/devtree.c

@@ -0,0 +1,297 @@
+/*
+ * Copyright (C) 2025 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * Devicetree bus
+ *
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <ipxe/device.h>
+#include <ipxe/fdt.h>
+#include <ipxe/devtree.h>
+
+static struct dt_driver dt_node_driver __dt_driver;
+struct root_device dt_root_device __root_device;
+
+static void dt_remove_children ( struct dt_device *parent );
+
+/**
+ * Find devicetree driver
+ *
+ * @v dt		Devicetree device
+ * @v offset		Starting node offset
+ * @ret driver		Driver, or NULL
+ */
+static struct dt_driver * dt_find_driver ( struct dt_device *dt,
+					   unsigned int offset ) {
+	struct dt_driver *driver;
+	const char *ids;
+	const char *id;
+	unsigned int count;
+	unsigned int i;
+
+	/* Read compatible programming model identifiers */
+	ids = fdt_strings ( &sysfdt, offset, "compatible", &count );
+
+	/* Look for a compatible driver */
+	for ( id = ids ; count-- ; id += ( strlen ( id ) + 1 ) ) {
+		DBGC2 ( &sysfdt, "DT %s is compatible with %s\n",
+			dt->path, id );
+		for_each_table_entry ( driver, DT_DRIVERS ) {
+			for ( i = 0 ; i < driver->id_count ; i++ ) {
+				if ( strcmp ( id, driver->ids[i] ) == 0 ) {
+					DBGC ( dt, "DT %s has %s driver %s\n",
+					       dt->path, id, driver->name );
+					return driver;
+				}
+			}
+		}
+	}
+
+	return NULL;
+}
+
+/**
+ * Probe devicetree device
+ *
+ * @v dt		Devicetree device
+ * @v offset		Starting node offset
+ * @ret rc		Return status code
+ */
+static int dt_probe ( struct dt_device *dt, unsigned int offset ) {
+	struct dt_driver *driver = NULL;
+	int rc;
+
+	/* Identify driver.  Use the generic node driver if no other
+	 * driver matches, or if this is the root device (which has no
+	 * valid devicetree parent).
+	 */
+	if ( offset > 0 )
+		driver = dt_find_driver ( dt, offset );
+	if ( ! driver )
+		driver = &dt_node_driver;
+
+	/* Record driver */
+	dt->driver = driver;
+	dt->dev.driver_name = driver->name;
+
+	/* Probe device */
+	if ( ( rc = driver->probe ( dt, offset ) ) != 0 ) {
+		if ( driver != &dt_node_driver ) {
+			DBGC ( dt, "DT %s could not probe: %s\n",
+			       dt->path, strerror ( rc ) );
+		}
+		return rc;
+	}
+
+	return 0;
+}
+
+/**
+ * Remove devicetree device
+ *
+ * @v dt		Devicetree device
+ */
+static void dt_remove ( struct dt_device *dt ) {
+
+	/* Remove device */
+	dt->driver->remove ( dt );
+}
+
+/**
+ * Probe devicetree node
+ *
+ * @v parent		Parent device, or NULL for root of tree
+ * @v offset		Starting node offset
+ * @v name		Node name
+ * @ret rc		Return status code
+ */
+static int dt_probe_node ( struct dt_device *parent, unsigned int offset,
+			   const char *name ) {
+	struct dt_device *dt;
+	const char *ppath;
+	size_t path_len;
+	void *path;
+	int rc;
+
+	/* Allocate and initialise device */
+	ppath = ( ( parent && parent->path[1] ) ? parent->path : "" );
+	path_len = ( strlen ( ppath ) + 1 /* "/" */ +
+		     strlen ( name ) + 1 /* NUL */ );
+	dt = zalloc ( sizeof ( *dt ) + path_len );
+	if ( ! dt ) {
+		rc = -ENOMEM;
+		goto err_alloc;
+	}
+	path = ( ( ( void * ) dt ) + sizeof ( *dt ) );
+	sprintf ( path, "%s/%s", ppath, name );
+	dt->path = path;
+	snprintf ( dt->dev.name, sizeof ( dt->dev.name ), "%s", name );
+	dt->dev.desc.bus_type = BUS_TYPE_DT;
+	dt->dev.parent = ( parent ? &parent->dev : &dt_root_device.dev );
+	INIT_LIST_HEAD ( &dt->dev.children );
+	list_add_tail ( &dt->dev.siblings, &dt->dev.parent->children );
+
+	/* Probe device */
+	if ( ( rc = dt_probe ( dt, offset ) ) != 0 )
+		goto err_probe;
+
+	return 0;
+
+	dt_remove ( dt );
+ err_probe:
+	list_del ( &dt->dev.siblings );
+	free ( dt );
+ err_alloc:
+	return rc;
+}
+
+/**
+ * Remove devicetree node
+ *
+ * @v dt		Devicetree device
+ */
+static void dt_remove_node ( struct dt_device *dt ) {
+
+	/* Remove driver */
+	dt_remove ( dt );
+
+	/* Delete and free device */
+	list_del ( &dt->dev.siblings );
+	free ( dt );
+}
+
+/**
+ * Probe devicetree children
+ *
+ * @v parent		Parent device
+ * @v offset		Starting node offset
+ * @ret rc		Return status code
+ */
+static int dt_probe_children ( struct dt_device *parent,
+			       unsigned int offset ) {
+	struct fdt_descriptor desc;
+	int depth;
+	int rc;
+
+	/* Probe any immediate child nodes */
+	for ( depth = -1 ; ; depth += desc.depth, offset = desc.next ) {
+
+		/* Describe token */
+		if ( ( rc = fdt_describe ( &sysfdt, offset, &desc ) ) != 0 ) {
+			DBGC ( &sysfdt, "DT %s has malformed node: %s\n",
+			       parent->path, strerror ( rc ) );
+			goto err_describe;
+		}
+
+		/* Terminate when we exit this node */
+		if ( ( depth == 0 ) && ( desc.depth < 0 ) )
+			break;
+
+		/* Probe child node, if applicable */
+		if ( ( depth == 0 ) && desc.name && ( ! desc.data ) )
+			dt_probe_node ( parent, desc.offset, desc.name );
+	}
+
+	/* Fail if we have no children (so that this device will be freed) */
+	if ( list_empty ( &parent->dev.children ) ) {
+		rc = -ENODEV;
+		goto err_no_children;
+	}
+
+	return 0;
+
+ err_no_children:
+ err_describe:
+	dt_remove_children ( parent );
+	return rc;
+}
+
+/**
+ * Remove devicetree children
+ *
+ * @v parent		Parent device
+ */
+static void dt_remove_children ( struct dt_device *parent ) {
+	struct dt_device *dt;
+	struct dt_device *tmp;
+
+	/* Remove all child nodes */
+	list_for_each_entry_safe ( dt, tmp, &parent->dev.children,
+				   dev.siblings ) {
+		dt_remove_node ( dt );
+	}
+	assert ( list_empty ( &parent->dev.children ) );
+}
+
+/** Generic node driver */
+static struct dt_driver dt_node_driver __dt_driver = {
+	.name = "node",
+	.probe = dt_probe_children,
+	.remove = dt_remove_children,
+};
+
+/**
+ * Probe devicetree bus
+ *
+ * @v rootdev		Devicetree root device
+ * @ret rc		Return status code
+ */
+static int dt_probe_all ( struct root_device *rootdev __unused ) {
+
+	/* Probe root node */
+	return dt_probe_node ( NULL, 0, "" );
+}
+
+/**
+ * Remove devicetree bus
+ *
+ * @v rootdev		Devicetree root device
+ */
+static void dt_remove_all ( struct root_device *rootdev ) {
+	struct dt_device *dt;
+
+	/* Remove root node */
+	dt = list_first_entry ( &rootdev->dev.children, struct dt_device,
+				dev.siblings );
+	assert ( dt != NULL );
+	dt_remove_node ( dt );
+}
+
+/** Devicetree bus root device driver */
+static struct root_driver dt_root_driver = {
+	.probe = dt_probe_all,
+	.remove = dt_remove_all,
+};
+
+/** Devicetree bus root device */
+struct root_device dt_root_device __root_device = {
+	.dev = { .name = "DT" },
+	.driver = &dt_root_driver,
+};

src/include/ipxe/device.h

@@ -69,6 +69,9 @@ struct device_description {
 /** USB bus type */
 #define BUS_TYPE_USB 10
 
+/** Devicetree bus type */
+#define BUS_TYPE_DT 11
+
 /** A hardware device */
 struct device {
 	/** Name */

src/include/ipxe/devtree.h

@@ -0,0 +1,76 @@
+#ifndef _IPXE_DEVTREE_H
+#define _IPXE_DEVTREE_H
+
+/** @file
+ *
+ * Devicetree bus
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/device.h>
+
+/** A devicetree device */
+struct dt_device {
+	/** Generic device */
+	struct device dev;
+	/** Device path */
+	const char *path;
+	/** Driver for this device */
+	struct dt_driver *driver;
+	/** Driver-private data */
+	void *priv;
+};
+
+/** A devicetree driver */
+struct dt_driver {
+	/** Driver name */
+	const char *name;
+	/** Compatible programming model identifiers */
+	const char **ids;
+	/** Number of compatible programming model identifiers */
+	unsigned int id_count;
+	/**
+	 * Probe device
+	 *
+	 * @v dt		Devicetree device
+	 * @v offset		Starting node offset
+	 * @ret rc		Return status code
+	 */
+	int ( * probe ) ( struct dt_device *dt, unsigned int offset );
+	/**
+	 * Remove device
+	 *
+	 * @v dt		Devicetree device
+	 */
+	void ( * remove ) ( struct dt_device *dt );
+};
+
+/** Devicetree driver table */
+#define DT_DRIVERS __table ( struct dt_driver, "dt_drivers" )
+
+/** Declare a devicetree driver */
+#define __dt_driver __table_entry ( DT_DRIVERS, 01 )
+
+/**
+ * Set devicetree driver-private data
+ *
+ * @v dt		Devicetree device
+ * @v priv		Private data
+ */
+static inline void dt_set_drvdata ( struct dt_device *dt, void *priv ) {
+	dt->priv = priv;
+}
+
+/**
+ * Get devicetree driver-private data
+ *
+ * @v dt		Devicetree device
+ * @ret priv		Private data
+ */
+static inline void * dt_get_drvdata ( struct dt_device *dt ) {
+	return dt->priv;
+}
+
+#endif /* _IPXE_DEVTREE_H */

src/include/ipxe/errfile.h

@@ -231,6 +231,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_aqc1xx		     ( ERRFILE_DRIVER | 0x00d70000 )
 #define ERRFILE_atl_hw		     ( ERRFILE_DRIVER | 0x00d80000 )
 #define ERRFILE_atl2_hw		     ( ERRFILE_DRIVER | 0x00d90000 )
+#define ERRFILE_devtree		     ( ERRFILE_DRIVER | 0x00da0000 )
 
 #define ERRFILE_aoe			( ERRFILE_NET | 0x00000000 )
 #define ERRFILE_arp			( ERRFILE_NET | 0x00010000 )