[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/image/efi_image.c

@@ -33,6 +33,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/efi/efi_driver.h>
 #include <ipxe/efi/efi_image.h>
 #include <ipxe/efi/efi_shim.h>
+#include <ipxe/efi/efi_fdt.h>
 #include <ipxe/image.h>
 #include <ipxe/init.h>
 #include <ipxe/features.h>
@@ -122,6 +123,24 @@ static wchar_t * efi_image_cmdline ( struct image *image ) {
 	return cmdline;
 }
 
+/**
+ * Install EFI Flattened Device Tree table (when no FDT support is present)
+ *
+ * @ret rc		Return status code
+ */
+__weak int efi_fdt_install ( void ) {
+	return 0;
+}
+
+/**
+ * Uninstall EFI Flattened Device Tree table (when no FDT support is present)
+ *
+ * @ret rc		Return status code
+ */
+__weak int efi_fdt_uninstall ( void ) {
+	return 0;
+}
+
 /**
  * Execute EFI image
  *
@@ -187,6 +206,13 @@ static int efi_image_exec ( struct image *image ) {
 		goto err_download_install;
 	}
 
+	/* Install Flattened Device Tree table */
+	if ( ( rc = efi_fdt_install() ) != 0 ) {
+		DBGC ( image, "EFIIMAGE %s could not install FDT: %s\n",
+		       image->name, strerror ( rc ) );
+		goto err_fdt_install;
+	}
+
 	/* Create device path for image */
 	path = efi_image_path ( exec, snpdev->path );
 	if ( ! path ) {
@@ -313,6 +339,8 @@ static int efi_image_exec ( struct image *image ) {
  err_cmdline:
 	free ( path );
  err_image_path:
+	efi_fdt_uninstall();
+ err_fdt_install:
 	efi_download_uninstall ( snpdev->handle );
  err_download_install:
 	efi_pxe_uninstall ( snpdev->handle );

src/include/ipxe/efi/efi_fdt.h

@@ -0,0 +1,17 @@
+#ifndef _IPXE_EFI_FDT_H
+#define _IPXE_EFI_FDT_H
+
+/** @file
+ *
+ * EFI Flattened Device Tree
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#include <ipxe/efi/efi.h>
+
+extern int efi_fdt_install ( void );
+extern int efi_fdt_uninstall ( void );
+
+#endif /* _IPXE_EFI_FDT_H */

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;
+}