multiboot: Allow searching in volume 0 for redirect file

Searching in volume 0 is necessary for multiboot targets with only
one drive, like the M3K/Q1/ErosQ. Without this the search code will
never look at the redirect file on these targets.

The search bound is configured with a setting MULTIBOOT_MIN_VOLUME,
which defaults to 0, but is defined to 1 for Sansa players so they
keep their old behavior.

Change-Id: I6dc5cf98db4258731de2c68c3ab1182b4a4a655b

firmware/common/rb-loader.c

@@ -106,7 +106,7 @@ int load_firmware(unsigned char* buf, const char* firmware, int buffer_size)
          * 0 is the default boot volume, it is not checked here
          * if found <volume>/rockbox_main.<playername> and firmware
          * has a bootdata region this firmware will be loaded */
-        for (unsigned int i = NUM_VOLUMES - 1; i > 0 && ret < 0; i--)
+        for (int i = NUM_VOLUMES - 1; i >= MULTIBOOT_MIN_VOLUME && ret < 0; i--)
         {
             if (get_redirect_dir(filename, sizeof(filename), i,
                                  BOOTDIR, firmware) > 0)

firmware/export/config.h

@@ -869,6 +869,12 @@ Lyre prototype 1 */
 #define HAVE_MULTIBOOT
 #endif
 
+/* The lowest numbered volume to read a multiboot redirect from; default is to
+ * allow any volume but some targets may wish to exclude the internal drive. */
+#if defined(HAVE_MULTIBOOT) && !defined(MULTIBOOT_MIN_VOLUME)
+# define MULTIBOOT_MIN_VOLUME 0
+#endif
+
 #ifndef NUM_DRIVES
 #define NUM_DRIVES 1
 #endif

firmware/export/config/sansaclipplus.h

@@ -11,6 +11,7 @@
 #define HAVE_BOOTDATA
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.clip+"
+#define MULTIBOOT_MIN_VOLUME 1
 
 #define HAVE_MULTIDRIVE
 #define NUM_DRIVES 2

firmware/export/config/sansaclipzip.h

@@ -11,6 +11,7 @@
 #define HAVE_BOOTDATA
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.clipzip"
+#define MULTIBOOT_MIN_VOLUME 1
 
 #define HAVE_MULTIDRIVE
 #define NUM_DRIVES 2

firmware/export/config/sansae200.h

@@ -13,6 +13,7 @@
 
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.e200"
+#define MULTIBOOT_MIN_VOLUME 1
 
 /* define this if you have recording possibility */
 #define HAVE_RECORDING

firmware/export/config/sansafuze.h

@@ -10,6 +10,7 @@
 
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.fuze"
+#define MULTIBOOT_MIN_VOLUME 1
 
 #define HW_SAMPR_CAPS       SAMPR_CAP_ALL_96
 

firmware/export/config/sansafuzeplus.h

@@ -12,6 +12,7 @@
 #define HAVE_BOOTDATA
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.fuze+"
+#define MULTIBOOT_MIN_VOLUME 1
 
 // HW can do it but we don't have the IRAM for mix buffers
 //#define HW_SAMPR_CAPS       SAMPR_CAP_ALL_192

firmware/export/config/sansafuzev2.h

@@ -10,6 +10,7 @@
 
 /* define boot redirect file name allows booting from external drives */
 #define BOOT_REDIR "rockbox_main.fuze2"
+#define MULTIBOOT_MIN_VOLUME 1
 
 #define HW_SAMPR_CAPS       SAMPR_CAP_ALL_96