fastboot: Add "fastboot device" command for runtime block device selection

Add the ability to change the fastboot flash target device at runtime
without recompiling. This is useful for:

- Platforms with multiple storage options (eMMC + UFS + NVMe)
- Development and testing scenarios
- Recovery situations where the default device is unavailable

New command syntax:
  fastboot device <interface> <dev> - set flash interface and device
  fastboot device                   - show current interface and device

Implementation details:
- Add fastboot_block_set_interface() and fastboot_block_set_device()
  functions to set runtime values
- Add fastboot_block_get_interface() and fastboot_block_get_device()
  getters that return runtime value if set, otherwise fall back to
  Kconfig defaults
- Update fb_block.c to use the new getter functions
- Add command handler gated by CONFIG_FASTBOOT_FLASH_BLOCK

Example usage:
  => fastboot device scsi 0
  Set fastboot block interface to 'scsi', device to 0
  => fastboot usb 0
  (now flashing targets SCSI device 0 instead of default)

Change-Id: 7b54f839-5659-4aaf-b58f-d6107e08a24d
Signed-off-by: Anton Burticica <mouse@ya.ru>

Author: ya-mouse

cmd/fastboot.c

@@ -15,6 +15,9 @@
 #include <watchdog.h>
 #include <linux/printk.h>
 #include <linux/stringify.h>
+#if CONFIG_IS_ENABLED(FASTBOOT_FLASH_BLOCK)
+#include <fb_block.h>
+#endif
 
 #if CONFIG_IS_ENABLED(NET)
 static int do_fastboot_udp(int argc, char *const argv[],
@@ -119,6 +122,38 @@ static int do_fastboot_usb(int argc, char *const argv[],
 	return ret;
 }
 
+#if CONFIG_IS_ENABLED(FASTBOOT_FLASH_BLOCK)
+static int do_fastboot_device(int argc, char *const argv[])
+{
+	const char *interface;
+	int device;
+	char *endp;
+
+	if (argc < 3) {
+		/* Print current settings */
+		interface = fastboot_block_get_interface();
+		device = fastboot_block_get_device();
+		printf("fastboot block interface: %s, device: %d\n",
+		       interface && *interface ? interface : "(not set)", device);
+		return CMD_RET_SUCCESS;
+	}
+
+	interface = argv[1];
+	device = simple_strtoul(argv[2], &endp, 0);
+	if (*endp != '\0') {
+		pr_err("Error: Invalid device number\n");
+		return CMD_RET_FAILURE;
+	}
+
+	fastboot_block_set_interface(interface);
+	fastboot_block_set_device(device);
+	printf("Set fastboot block interface to '%s', device to %d\n",
+	       interface, device);
+
+	return CMD_RET_SUCCESS;
+}
+#endif
+
 static int do_fastboot(struct cmd_tbl *cmdtp, int flag, int argc,
 		       char *const argv[])
 {
@@ -154,6 +189,14 @@ static int do_fastboot(struct cmd_tbl *cmdtp, int flag, int argc,
 		;
 	}
 
+#if CONFIG_IS_ENABLED(FASTBOOT_FLASH_BLOCK)
+	if (argc > 0 && !strcmp(argv[1], "device")) {
+		argv++;
+		argc--;
+		return do_fastboot_device(argc, argv);
+	}
+#endif
+
 	/* Handle case when USB controller param is just '-' */
 	if (argc == 1) {
 		pr_err("Error: Incorrect USB controller index\n");
@@ -179,7 +222,18 @@ static int do_fastboot(struct cmd_tbl *cmdtp, int flag, int argc,
 U_BOOT_CMD(
 	fastboot, CONFIG_SYS_MAXARGS, 1, do_fastboot,
 	"run as a fastboot usb or udp device",
-	"[-l addr] [-s size] usb <controller> | udp\n"
+	"[-l addr] [-s size] usb <controller>"
+#if IS_ENABLED(CONFIG_TCP_FUNCTION_FASTBOOT)
+	" | tcp"
+#endif
+#if IS_ENABLED(CONFIG_UDP_FUNCTION_FASTBOOT)
+	" | udp"
+#endif
+#if CONFIG_IS_ENABLED(FASTBOOT_FLASH_BLOCK)
+	"\nfastboot device <interface> <dev> - set flash interface and device"
+	"\nfastboot device                   - show current interface and device"
+#endif
+	"\n"
 	"\taddr - address of buffer used during data transfers ("
 	__stringify(CONFIG_FASTBOOT_BUF_ADDR) ")\n"
 	"\tsize - size of buffer used during data transfers ("

drivers/fastboot/fb_block.c

@@ -12,6 +12,43 @@
 #include <malloc.h>
 #include <part.h>
 
+/**
+ * fastboot_block_interface - runtime block interface name
+ */
+static char fastboot_block_interface[16];
+
+/**
+ * fastboot_block_device - runtime block device ID
+ */
+static int fastboot_block_device = -1;
+
+void fastboot_block_set_interface(const char *interface)
+{
+	strncpy(fastboot_block_interface, interface, 16);
+}
+
+const char *fastboot_block_get_interface(void)
+{
+	if (*fastboot_block_interface)
+		return fastboot_block_interface;
+	return config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
+				  CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
+				  NULL);
+}
+
+void fastboot_block_set_device(int device)
+{
+	fastboot_block_device = device;
+}
+
+int fastboot_block_get_device(void)
+{
+	if (fastboot_block_device >= 0)
+		return fastboot_block_device;
+	return config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
+				  CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
+}
+
 /**
  * FASTBOOT_MAX_BLOCKS_ERASE - maximum blocks to erase per derase call
  *
@@ -125,11 +162,8 @@ int fastboot_block_get_part_info(const char *part_name,
 				 char *response)
 {
 	int ret;
-	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
-						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
-						   NULL);
-	const int device = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
-					      CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
+	const char *interface = fastboot_block_get_interface();
+	const int device = fastboot_block_get_device();
 
 	if (!part_name || !strcmp(part_name, "")) {
 		fastboot_fail("partition not given", response);

include/fb_block.h

@@ -102,4 +102,32 @@ void fastboot_block_write_sparse_image(struct blk_desc *dev_desc, struct disk_pa
 void fastboot_block_flash_write(const char *part_name, void *download_buffer,
 				u32 download_bytes, char *response);
 
+/**
+ * fastboot_block_set_interface() - Set the block interface name
+ *
+ * @interface: Interface name (e.g., "mmc", "scsi", "nvme")
+ */
+void fastboot_block_set_interface(const char *interface);
+
+/**
+ * fastboot_block_get_interface() - Get the block interface name
+ *
+ * Return: Interface name, or config default if not set
+ */
+const char *fastboot_block_get_interface(void);
+
+/**
+ * fastboot_block_set_device() - Set the block device ID
+ *
+ * @device: Device ID number
+ */
+void fastboot_block_set_device(int device);
+
+/**
+ * fastboot_block_get_device() - Get the block device ID
+ *
+ * Return: Device ID, or config default if not set
+ */
+int fastboot_block_get_device(void);
+
 #endif // _FB_BLOCK_H_