From: Svyatoslav Ryhel <clamor95@gmail.com>
Date: Thu, 25 Jan 2024 20:16:54 +0000 (+0200)
Subject: boot: pxe_utils: skip fdt setup in case legacy kernel is booted
X-Git-Url: http://git.dujemihanovic.xyz/img/static/git-favicon.png?a=commitdiff_plain;h=c95e948870bdfc606946174facd9ea359ce84e58;p=u-boot.git

boot: pxe_utils: skip fdt setup in case legacy kernel is booted

Currently, if boot with extlinux.conf and do not set the fdt
U-Boot will provide its own device tree. This behavior is
beneficial if the U-Boot device tree is in sync with Linux,
but it totally halts the booting of pre-dtb kernels (3.4 for
example) since it uses ATAGs. To fix this, pass `-` in the
fdt extlinux field as a signal that no tree should be used.

Suggested-by: Jonas Schwöbel <jonasschwoebel@yahoo.de>
Tested-by: Jethro Bull <jethrob@hotmail.com>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
---

diff --git a/boot/pxe_utils.c b/boot/pxe_utils.c
index 83bc167785..9620562675 100644
--- a/boot/pxe_utils.c
+++ b/boot/pxe_utils.c
@@ -634,7 +634,12 @@ static int label_boot(struct pxe_context *ctx, struct pxe_label *label)
 		char *fdtfilefree = NULL;
 
 		if (label->fdt) {
-			fdtfile = label->fdt;
+			if (IS_ENABLED(CONFIG_SUPPORT_PASSING_ATAGS)) {
+				if (strcmp("-", label->fdt))
+					fdtfile = label->fdt;
+			} else {
+				fdtfile = label->fdt;
+			}
 		} else if (label->fdtdir) {
 			char *f1, *f2, *f3, *f4, *slash;
 
@@ -731,14 +736,26 @@ static int label_boot(struct pxe_context *ctx, struct pxe_label *label)
 		zboot_argc = 5;
 	}
 
-	if (!bootm_argv[3])
-		bootm_argv[3] = env_get("fdt_addr");
+	if (!bootm_argv[3]) {
+		if (IS_ENABLED(CONFIG_SUPPORT_PASSING_ATAGS)) {
+			if (strcmp("-", label->fdt))
+				bootm_argv[3] = env_get("fdt_addr");
+		} else {
+			bootm_argv[3] = env_get("fdt_addr");
+		}
+	}
 
 	kernel_addr_r = genimg_get_kernel_addr(kernel_addr);
 	buf = map_sysmem(kernel_addr_r, 0);
 
-	if (!bootm_argv[3] && genimg_get_format(buf) != IMAGE_FORMAT_FIT)
-		bootm_argv[3] = env_get("fdtcontroladdr");
+	if (!bootm_argv[3] && genimg_get_format(buf) != IMAGE_FORMAT_FIT) {
+		if (IS_ENABLED(CONFIG_SUPPORT_PASSING_ATAGS)) {
+			if (strcmp("-", label->fdt))
+				bootm_argv[3] = env_get("fdtcontroladdr");
+		} else {
+			bootm_argv[3] = env_get("fdtcontroladdr");
+		}
+	}
 
 	if (bootm_argv[3]) {
 		if (!bootm_argv[2])
diff --git a/doc/develop/distro.rst b/doc/develop/distro.rst
index 8016acad09..9e715b23eb 100644
--- a/doc/develop/distro.rst
+++ b/doc/develop/distro.rst
@@ -81,6 +81,12 @@ as specified at `Boot Loader Specification`_:
 * Does not document the fdtdir option, which automatically selects the DTB to
   pass to the kernel.
 
+* If no fdt/fdtdir is provided, the U-Boot will pass its own currently used
+  device tree.
+
+* If ``-`` is passed as fdt argument and ``CONFIG_SUPPORT_PASSING_ATAGS`` is
+  enabled, then no device tree will be used (legacy booting / pre-dtb kernel).
+
 See also doc/README.pxe under 'pxe file format'.
 
 One example extlinux.conf generated by the Fedora installer is::