Change default to load embedded DTB on matching compatible

README.md

@@ -18,6 +18,11 @@ lookup table in the .hwids section of the kernel image.
 If a match is found it loads the corresponding device tree from the
 .dtbauto section before jumping tothe bundled kernel.
 
+## Command-line parameters
+
+- `debug`: Enable debug logging
+- `stubble.dtb_override=true/false`: Enable or disable device-tree compat based dtb lookup. The default is `true`.
+
 ## Dependencies
 
 ```

include/pe.h

@@ -3,6 +3,8 @@
 
 #include "efi.h"
 
+extern bool dtb_override;
+
 /* This is the actual PE format of the section header */
 typedef struct PeSectionHeader {
         uint8_t  Name[8];

pe.c

@@ -35,6 +35,8 @@
 #  define TARGET_MACHINE_TYPE_COMPATIBILITY 0
 #endif
 
+bool dtb_override = true;
+
 typedef struct DosFileHeader {
         uint8_t  Magic[2];
         uint16_t LastSize;
@@ -203,7 +205,18 @@ static bool pe_use_this_dtb(
 
         EFI_STATUS err;
 
-	/* Do nothing if a firmware dtb exists */
+        if (dtb_override == true) {
+                err = devicetree_match(dtb, dtb_size);
+                if (err == EFI_SUCCESS) {
+                        log_debug("found device-tree based on compatible: %s",
+                                        devicetree_get_compatible(dtb));
+                        return true;
+                }
+                if (err != EFI_UNSUPPORTED)
+                        return false;
+        }
+
+        /* Do nothing if a firmware dtb exists */
         const void *fw_dtb = find_configuration_table(MAKE_GUID_PTR(EFI_DTB_TABLE));
         if (fw_dtb)
                 return false;

stub.c

@@ -14,18 +14,29 @@
 
 DECLARE_SBAT(SBAT_STUB_SECTION_TEXT);
 
-static void parse_cmdline(char16_t *p) {
+static bool parse_string(char16_t *p, const char16_t *opt) {
+        const size_t opt_len = strlen16(opt);
+        if (strncmp16(p, opt, opt_len) == 0 &&
+                        (p[opt_len] == ' ' ||
+                         p[opt_len] == '\0'))
+                return true;
+        return false;
+}
 
+static void parse_cmdline(char16_t *p) {
         assert(p);
-
         while (*p != '\0') {
-                const char16_t *debug = L"debug";
-                size_t debug_len = strlen16(debug);
-                if (strncmp16(p, debug, debug_len) == 0 &&
-                                (p[debug_len] == ' ' ||
-                                 p[debug_len] == '\0'))
+                if (parse_string(p, L"debug")) {
                         log_isdebug = true;
-
+                } else if (strncmp16(p, L"stubble.dtb_override=",
+                                        strlen16(L"stubble.dtb_override=")) == 0) {
+                        p += strlen16(L"stubble.dtb_override=");
+                        if (parse_string(p, L"true")) {
+                                dtb_override = true;
+                        } else if (parse_string(p, L"false")) {
+                                dtb_override = false;
+                        }
+                }
                 p = strchr16(p, ' ');
                 if (p == NULL)
                         return;
@@ -155,6 +166,11 @@ static EFI_STATUS run(EFI_HANDLE image) {
          * as potential command line to use. */
         (void) process_arguments(image, loaded_image, &cmdline);
         parse_cmdline(cmdline);
+        if (log_isdebug == true) {
+                log_debug("Stubble configuration:");
+                log_debug("debug: enabled");
+                log_debug("dtb_override: %s", dtb_override ? "enabled" : "disabled");
+        }
 
         /* Find the sections we want to operate on */
         err = find_sections(loaded_image, sections);