usb: remove "Ask" USB Mode (FS#13317)

USB ask mode is basically a footgun: it can't work on native targets
and doesn't work reliably on hosted ones, and it continually produces
a slow trickle of problems. FS#13317 gives a rundown of the issues.
Removing the setting seems like the best solution for now, since a fix
would be pretty involved.

This partially reverts 60f581e8f5. The USB Mode setting is left in
place so the option can be added back later in a non-buggy way.

Change-Id: Ie01b28dd2ed95a31b509a7834d85bac8eb866098

apps/settings_list.c

@@ -2148,19 +2148,18 @@ const struct settings_list settings[] = {
                    LANG_USB_MODE,
                    USBMODE_DEFAULT,
                    "usb mode",
-                   "ask,mass storage,charge"
+                   "mass storage,charge"
 #if defined(DX50) || defined(DX90)
                    ",adb"
 #endif
                    ,
 #if defined(DX50) || defined(DX90)
                    ibasso_set_usb_mode,
-                   4,
+                   3,
 #else
                    usb_set_mode,
-                   3,
+                   2,
 #endif
-                   ID2P(LANG_ASK),
                    ID2P(LANG_USB_MODE_MASS_STORAGE),
                    ID2P(LANG_USB_MODE_CHARGE)
 #if defined(DX50) || defined(DX90)

firmware/export/usb.h

@@ -134,7 +134,6 @@ enum
 /* Supported usb modes. */
 enum
 {
-    USB_MODE_ASK = 0,
     USB_MODE_MASS_STORAGE,
     USB_MODE_CHARGE,
     USB_MODE_ADB

firmware/usb.c

@@ -491,37 +491,12 @@ static void NORETURN_ATTR usb_thread(void)
                 if (button_status() & ~USBPOWER_BTN_IGNORE)
                     new_usbmode = USB_MODE_MASS_STORAGE;
                 break;
-#ifndef BOOTLOADER
-            case USB_MODE_ASK:
-                new_usbmode = USB_MODE_ASK;
-                break;
-#endif
             default:
             case USB_MODE_MASS_STORAGE:
                 if (button_status() & ~USBPOWER_BTN_IGNORE)
                     new_usbmode = USB_MODE_CHARGE;
                 break;
 	    }
-
-#ifndef BOOTLOADER
-            if (new_usbmode == USB_MODE_ASK)
-            {
-                push_current_activity(ACTIVITY_USBSCREEN);
-                if (yesno_pop(ID2P(LANG_ENTER_USB_STORAGE_MODE_QUERY)))
-                    new_usbmode = USB_MODE_MASS_STORAGE;
-                else
-                    new_usbmode = USB_MODE_CHARGE;
-                pop_current_activity();
-                /* Force full redraw */
-//                queue_post(&button_queue, BUTTON_REDRAW, 0);
-// Alternative approach, as above is supposedly inadequate by design.
-                FOR_NB_SCREENS(i)
-                {
-                    struct screen *screen = &screens[i];
-                    screen->set_viewport(NULL);
-                }
-            }
-#endif
 #endif
 
 #ifndef USB_DETECT_BY_REQUEST

manual/configure_rockbox/system_options.tex

@@ -870,8 +870,14 @@ therefore result in better runtime.
 \opt{usb_power}{
   \subsection{USB Mode}
     This controls what happens with the \dap{}'s USB port is connected.
-    \setting{Charge Only} and \setting{Mass Storage} will automatically enter
+    \setting{Mass Storage} allows you to transfer files, while
-    that mode, and \setting{Ask} will prompt the user each time.
+    \setting{Charge Only} will only charge the battery (and allow you to keep
+    using the player). You can choose the opposite behavior by holding down any
+    button while plugging in the USB cable.
+    \nopt{fuzeplus}{
+    \note{Be aware that holding a button may still perform its normal function,
+    so it is recommended to use a button without harmful side effects, such as
+    \ActionStdUsbCharge{}.}
 }
 \opt{multidrive_usb}{
   \subsection{USB Hide Internal Drive}

manual/rockbox_interface/main.tex

@@ -848,16 +848,13 @@ properly.}
 
   \opt{usb_power}{
     \section{USB Charging}
-    Whenever your \dap{} is connected to USB, it will automatically charge.
+    Your \dap{} will automatically charge when connected to USB. By default
-    However, depending on the \config{usb\_mode} setting, the \dap{} may also
+    Rockbox will connect in mass storage mode to transfer files, but you can
-    enter mass storage mode or prompt the user for what action to take.
+    prevent this by holding down any button while plugging in the USB cable,
-    When the \dap{} is configured to enter mass storage mode or automatically
+    or by changing the \setting{USB Mode} setting to \setting{Charge Only}.
-    charge, you may trigger the opposite behavior by holding down any button
-    while plugging it in.  Your \dap{} must already be in Rockbox for this to
-    function.
     \nopt{fuzeplus}{
-    \note{Be aware that this button may still perform its normal function, so
+    \note{Be aware that holding a button may still perform its normal function,
-    it is recommended to use a button without harmful side effects, such as
+    so it is recommended to use a button without harmful side effects, such as
     \ActionStdUsbCharge{}.}
     }
   }