From b20f506a7217ce18f08ec007467365f9e118c445 Mon Sep 17 00:00:00 2001
From: Michael Brown
Date: Fri, 28 Mar 2025 14:20:44 +0000
Subject: [efi] Install a device tree for the booted OS, if available

If we have a device tree available (e.g. because the user has
explicitly downloaded a device tree using the "fdt" command), then
provide it to the booted operating system as an EFI configuration
table.

Since x86 does not typically use device trees, we create weak symbols
for efi_fdt_install() and efi_fdt_uninstall() to avoid dragging FDT
support into all x86 UEFI binaries.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/interface/efi/efi_fdt.c | 82 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

(limited to 'src/interface')

diff --git a/src/interface/efi/efi_fdt.c b/src/interface/efi/efi_fdt.c
index 71b788ae7..4a10236a0 100644
--- a/src/interface/efi/efi_fdt.c
+++ b/src/interface/efi/efi_fdt.c
@@ -24,9 +24,12 @@
 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <string.h>
+#include <byteswap.h>
 #include <ipxe/fdt.h>
 #include <ipxe/init.h>
 #include <ipxe/efi/efi.h>
+#include <ipxe/efi/efi_table.h>
+#include <ipxe/efi/efi_fdt.h>
 #include <ipxe/efi/Guid/Fdt.h>
 
 /** @file
@@ -76,3 +79,82 @@ static void efi_fdt_init ( void ) {
 struct init_fn efi_fdt_init_fn __init_fn ( INIT_EARLY ) = {
 	.initialise = efi_fdt_init,
 };
+
+/**
+ * Determine length of EFI Flattened Device Tree
+ *
+ * @v data		Configuration table data (presumed valid)
+ * @ret len		Length of table
+ */
+static size_t efi_fdt_len ( const void *data ) {
+	const struct fdt_header *hdr = data;
+
+	return be32_to_cpu ( hdr->totalsize );
+}
+
+/** EFI Flattened Device Tree table type */
+static struct efi_table efi_fdt_table = {
+	.guid = &efi_fdt_table_guid,
+	.len = efi_fdt_len,
+};
+
+/** EFI Flattened Device Tree table backup */
+static void *efi_fdt_backup;
+
+/** EFI Flattened Device Tree installed table */
+static struct fdt_header *efi_fdt_installed;
+
+/**
+ * Install EFI Flattened Device Tree table
+ *
+ * @ret rc		Return status code
+ */
+int efi_fdt_install ( void ) {
+	int rc;
+
+	/* Create device tree */
+	if ( ( rc = fdt_create ( &efi_fdt_installed ) ) != 0 ) {
+		DBGC ( &efi_fdt, "EFI_FDT could not install: %s\n",
+		       strerror ( rc ) );
+		goto err_create;
+	}
+
+	/* Install table */
+	if ( ( rc = efi_install_table ( &efi_fdt_table, efi_fdt_installed,
+					&efi_fdt_backup ) ) != 0 ) {
+		DBGC ( &efi_fdt, "EFIFDT could not install: %s\n",
+		       strerror ( rc ) );
+		goto err_install;
+	}
+
+	return 0;
+
+	efi_uninstall_table ( &efi_fdt_table, &efi_fdt_backup );
+ err_install:
+	fdt_remove ( efi_fdt_installed );
+ err_create:
+	return rc;
+}
+
+/**
+ * Uninstall EFI Flattened Device Tree table
+ *
+ * @ret rc		Return status code
+ */
+int efi_fdt_uninstall ( void ) {
+	int rc;
+
+	/* Uninstall table */
+	if ( ( rc = efi_uninstall_table ( &efi_fdt_table,
+					  &efi_fdt_backup ) ) != 0 ) {
+		DBGC ( &efi_fdt, "EFIFDT could not %sinstall: %s\n",
+		       ( efi_fdt_backup ? "re" : "un" ), strerror ( rc ) );
+		/* Leak memory: there is nothing else we can do */
+		return rc;
+	}
+
+	/* Remove table */
+	fdt_remove ( efi_fdt_installed );
+
+	return 0;
+}
-- 
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