bootstd: Add the concept of a bootdev hunter

Some bootdevs must be enumerated before they appear. For example, USB
bootdevs are not visible until USB is enumerated.

With standard boot this needs to happen automatically, since we only
want to enumerate a bus if it is needed.

Add a way to define bootdev 'hunters' which can be used to hunt for
bootdevs of a given type. Track which ones have been used and add a
command to list them.

Include a clang work-around which seems to be needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/bootdev-uclass.c b/boot/bootdev-uclass.c
index 0ef3daf..62eb0b6 100644
--- a/boot/bootdev-uclass.c
+++ b/boot/bootdev-uclass.c
@@ -636,6 +636,37 @@
 	return 0;
 }
 
+void bootdev_list_hunters(struct bootstd_priv *std)
+{
+	struct bootdev_hunter *orig, *start;
+	int n_ent, i;
+
+	orig = ll_entry_start(struct bootdev_hunter, bootdev_hunter);
+	n_ent = ll_entry_count(struct bootdev_hunter, bootdev_hunter);
+
+	/*
+	 * workaround for strange bug in clang-12 which sees all the below data
+	 * as zeroes. Any access of start seems to fix it, such as
+	 *
+	 *    printf("%p", start);
+	 *
+	 * Use memcpy() to force the correct behaviour.
+	 */
+	memcpy(&start, &orig, sizeof(orig));
+	printf("%4s  %4s  %-15s  %s\n", "Prio", "Used", "Uclass", "Hunter");
+	printf("%4s  %4s  %-15s  %s\n", "----", "----", "---------------", "---------------");
+	for (i = 0; i < n_ent; i++) {
+		struct bootdev_hunter *info = start + i;
+
+		printf("%4d  %4s  %-15s  %s\n", info->prio,
+		       std->hunters_used & BIT(i) ? "*" : "",
+		       uclass_get_name(info->uclass),
+		       info->drv ? info->drv->name : "(none)");
+	}
+
+	printf("(total hunters: %d)\n", n_ent);
+}
+
 static int bootdev_post_bind(struct udevice *dev)
 {
 	struct bootdev_uc_plat *ucp = dev_get_uclass_plat(dev);
diff --git a/cmd/bootdev.c b/cmd/bootdev.c
index ecd797c..80bfe28 100644
--- a/cmd/bootdev.c
+++ b/cmd/bootdev.c
@@ -107,14 +107,43 @@
 	return 0;
 }
 
+static int do_bootdev_hunt(struct cmd_tbl *cmdtp, int flag, int argc,
+			   char *const argv[])
+{
+	struct bootstd_priv *priv;
+	const char *spec = NULL;
+	bool list = false;
+	int ret = 0;
+
+	if (argc >= 2) {
+		if (!strcmp(argv[1], "-l"))
+			list = true;
+		else
+			spec = argv[1];
+	}
+
+	ret = bootstd_get_priv(&priv);
+	if (ret)
+		return ret;
+	if (list) {
+		bootdev_list_hunters(priv);
+	} else {
+		/* TODO: implement hunting */
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_SYS_LONGHELP
 static char bootdev_help_text[] =
-	"list [-p]      - list all available bootdevs (-p to probe)\n"
-	"bootdev select <bd>    - select a bootdev by name | label | seq\n"
-	"bootdev info [-p]      - show information about a bootdev (-p to probe)";
+	"list [-p]         - list all available bootdevs (-p to probe)\n"
+	"bootdev hunt [-l|<spec>]  - use hunt drivers to find bootdevs\n"
+	"bootdev select <bd>       - select a bootdev by name | label | seq\n"
+	"bootdev info [-p]         - show information about a bootdev (-p to probe)";
 #endif
 
 U_BOOT_CMD_WITH_SUBCMDS(bootdev, "Boot devices", bootdev_help_text,
 	U_BOOT_SUBCMD_MKENT(list, 2, 1, do_bootdev_list),
+	U_BOOT_SUBCMD_MKENT(hunt, 2, 1, do_bootdev_hunt),
 	U_BOOT_SUBCMD_MKENT(select, 2, 1, do_bootdev_select),
 	U_BOOT_SUBCMD_MKENT(info, 2, 1, do_bootdev_info));
diff --git a/include/bootdev.h b/include/bootdev.h
index 1e91d41..cafb528 100644
--- a/include/bootdev.h
+++ b/include/bootdev.h
@@ -11,6 +11,7 @@
 
 struct bootflow;
 struct bootflow_iter;
+struct bootstd_priv;
 struct udevice;
 
 /**
@@ -33,6 +34,53 @@
 	BOOTDEVP_COUNT,
 };
 
+struct bootdev_hunter;
+
+/**
+ * bootdev_hunter_func - function to probe for bootdevs of a given type
+ *
+ * This should hunt around for bootdevs of the given type, binding them as it
+ * finds them. This may involve bus enumeration, etc.
+ *
+ * @info: Info structure describing this hunter
+ * @show: true to show information from the hunter
+ * Returns: 0 if OK, -ve on error
+ */
+typedef int (*bootdev_hunter_func)(struct bootdev_hunter *info, bool show);
+
+/**
+ * struct bootdev_hunter - information about how to hunt for bootdevs
+ *
+ * @prio: Scanning priority of this hunter
+ * @uclass: Uclass ID for the media associated with this bootdev
+ * @drv: bootdev driver for the things found by this hunter
+ * @hunt: Function to call to hunt for bootdevs of this type (NULL if none)
+ *
+ * Some bootdevs are not visible until other devices are enumerated. For
+ * example, USB bootdevs only appear when the USB bus is enumerated.
+ *
+ * On the other hand, we don't always want to enumerate all the buses just to
+ * find the first valid bootdev. Ideally we want to work through them in
+ * priority order, so that the fastest bootdevs are discovered first.
+ *
+ * This struct holds information about the bootdev so we can determine the probe
+ * order and how to hunt for bootdevs of this type
+ */
+struct bootdev_hunter {
+	enum bootdev_prio_t prio;
+	enum uclass_id uclass;
+	struct driver *drv;
+	bootdev_hunter_func hunt;
+};
+
+/* declare a new bootdev hunter */
+#define BOOTDEV_HUNTER(__name)						\
+	ll_entry_declare(struct bootdev_hunter, __name, bootdev_hunter)
+
+/* access a bootdev hunter by name */
+#define BOOTDEV_HUNTER_GET(__name)						\
+	ll_entry_get(struct bootdev_hunter, __name, bootdev_hunter)
+
 /**
  * struct bootdev_uc_plat - uclass information about a bootdev
  *
@@ -205,6 +253,16 @@
  */
 int bootdev_setup_iter_order(struct bootflow_iter *iter, struct udevice **devp);
 
+/**
+ * bootdev_list_hunters() - List the available bootdev hunters
+ *
+ * These provide a way to find new bootdevs by enumerating buses, etc. This
+ * function lists the available hunters
+ *
+ * @std: Pointer to bootstd private info
+ */
+void bootdev_list_hunters(struct bootstd_priv *std);
+
 #if CONFIG_IS_ENABLED(BOOTSTD)
 /**
  * bootdev_setup_for_dev() - Bind a new bootdev device (deprecated)
diff --git a/include/bootstd.h b/include/bootstd.h
index bd30509..dddb3e1 100644
--- a/include/bootstd.h
+++ b/include/bootstd.h
@@ -33,6 +33,8 @@
  * @bootmeth_order: List of bootmeth devices to use, in order, NULL-terminated
  * @vbe_bootmeth: Currently selected VBE bootmeth, NULL if none
  * @theme: Node containing the theme information
+ * @hunters_used: Bitmask of used hunters, indexed by their position in the
+ * linker list. The bit is set if the hunter has been used already
  */
 struct bootstd_priv {
 	const char **prefixes;
@@ -45,6 +47,7 @@
 	struct udevice **bootmeth_order;
 	struct udevice *vbe_bootmeth;
 	ofnode theme;
+	uint hunters_used;
 };
 
 /**
diff --git a/test/boot/bootdev.c b/test/boot/bootdev.c
index 1c2a79f..a8ca12a 100644
--- a/test/boot/bootdev.c
+++ b/test/boot/bootdev.c
@@ -221,3 +221,55 @@
 	return 0;
 }
 BOOTSTD_TEST(bootdev_test_prio, UT_TESTF_DM | UT_TESTF_SCAN_FDT);
+
+/* Check listing hunters */
+static int bootdev_test_hunter(struct unit_test_state *uts)
+{
+	struct bootstd_priv *std;
+
+	/* get access to the used hunters */
+	ut_assertok(bootstd_get_priv(&std));
+
+	console_record_reset_enable();
+	bootdev_list_hunters(std);
+	ut_assert_nextline("Prio  Used  Uclass           Hunter");
+	ut_assert_nextlinen("----");
+	ut_assert_nextline("(total hunters: 0)");
+	ut_assert_console_end();
+
+	return 0;
+}
+BOOTSTD_TEST(bootdev_test_hunter, UT_TESTF_DM | UT_TESTF_SCAN_FDT);
+
+/* Check 'bootdev hunt' command */
+static int bootdev_test_cmd_hunt(struct unit_test_state *uts)
+{
+	struct bootstd_priv *std;
+
+	/* get access to the used hunters */
+	ut_assertok(bootstd_get_priv(&std));
+
+	console_record_reset_enable();
+	ut_assertok(run_command("bootdev hunt -l", 0));
+	ut_assert_nextline("Prio  Used  Uclass           Hunter");
+	ut_assert_nextlinen("----");
+	ut_assert_nextline("(total hunters: 0)");
+	ut_assert_console_end();
+
+	/* Scan all hunters */
+	ut_assertok(run_command("bootdev hunt", 0));
+	ut_assert_console_end();
+
+	/* List available hunters */
+	ut_assertok(run_command("bootdev hunt -l", 0));
+	ut_assert_nextlinen("Prio");
+	ut_assert_nextlinen("----");
+	ut_assert_nextline("(total hunters: 0)");
+	ut_assert_console_end();
+
+	ut_asserteq(0, std->hunters_used);
+
+	return 0;
+}
+BOOTSTD_TEST(bootdev_test_cmd_hunt, UT_TESTF_DM | UT_TESTF_SCAN_FDT |
+	     UT_TESTF_ETH_BOOTDEV);