arm/efi: Introduce xen,uefi-cfg-load DT property

Introduce the xen,uefi-cfg-load DT property of /chosen
node for ARM whose presence decide whether to force
the load of the UEFI Xen configuration file.

The logic is that if any multiboot,module is found in
the DT, then the xen,uefi-cfg-load property is used to see
if the UEFI Xen configuration file is needed.

Modify a comment in efi_arch_use_config_file, removing
the part that states "dom0 required" because it's not
true anymore with this commit.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

docs/misc/arm/device-tree/booting.txt

@@ -121,6 +121,14 @@ A Xen-aware bootloader would set xen,xen-bootargs for Xen, xen,dom0-bootargs
 for Dom0 and bootargs for native Linux.
 
 
+UEFI boot and DT
+================
+
+When Xen is booted using UEFI, it doesn't read the configuration file if any
+multiboot module is specified. To force Xen to load the configuration file, the
+boolean property xen,uefi-cfg-load must be declared in the /chosen node.
+
+
 Creating Multiple Domains directly from Xen
 ===========================================
 

docs/misc/efi.pandoc

@@ -14,6 +14,8 @@ loaded the modules and describes them in the device tree provided to Xen.  If a
 bootloader provides a device tree containing modules then any configuration
 files are ignored, and the bootloader is responsible for populating all
 relevant device tree nodes.
+The property "xen,uefi-cfg-load" can be specified in the /chosen node to force
+Xen to load the configuration file even if multiboot modules are found.
 
 Once built, `make install-xen` will place the resulting binary directly into
 the EFI boot partition, provided `EFI_VENDOR` is set in the environment (and

xen/arch/arm/efi/efi-boot.h

@@ -581,22 +581,40 @@ static void __init efi_arch_load_addr_check(EFI_LOADED_IMAGE *loaded_image)
 
 static bool __init efi_arch_use_config_file(EFI_SYSTEM_TABLE *SystemTable)
 {
+    bool load_cfg_file = true;
     /*
      * For arm, we may get a device tree from GRUB (or other bootloader)
      * that contains modules that have already been loaded into memory.  In
-     * this case, we do not use a configuration file, and rely on the
-     * bootloader to have loaded all required modules and appropriate
-     * options.
+     * this case, we search for the property xen,uefi-cfg-load in the /chosen
+     * node to decide whether to skip the UEFI Xen configuration file or not.
      */
 
     fdt = lookup_fdt_config_table(SystemTable);
     dtbfile.ptr = fdt;
     dtbfile.need_to_free = false; /* Config table memory can't be freed. */
-    if ( !fdt || fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") < 0 )
+
+    if ( fdt_node_offset_by_compatible(fdt, 0, "multiboot,module") > 0 )
+    {
+        /* Locate chosen node */
+        int node = fdt_subnode_offset(fdt, 0, "chosen");
+        const void *cfg_load_prop;
+        int cfg_load_len;
+
+        if ( node > 0 )
+        {
+            /* Check if xen,uefi-cfg-load property exists */
+            cfg_load_prop = fdt_getprop(fdt, node, "xen,uefi-cfg-load",
+                                        &cfg_load_len);
+            if ( !cfg_load_prop )
+                load_cfg_file = false;
+        }
+    }
+
+    if ( !fdt || load_cfg_file )
     {
         /*
          * We either have no FDT, or one without modules, so we must have a
-         * Xen EFI configuration file to specify modules.  (dom0 required)
+         * Xen EFI configuration file to specify modules.
          */
         return true;
     }