Fixed bug 5161 - Autodetect controller mappings based on the Linux Gamepad Specification

Jan Bujak

I wrote a new driver for my gamepad on Linux. I'd like SDL to support it out-of-box, as currently it just treats it as a generic joystick instead of a gamepad. From what I can see the only way to do that is to either 1) pick one of the already supported controllers' PID, VID and button layouts and have my driver send that (effectively lying that it's something else), or 2) submit a preconfigured, hardcoded mapping to SDL.

Both of those, in my opinion, are silly when we already have the Linux Gamepad Specification which standarizes this:

https://www.kernel.org/doc/html/v4.15/input/gamepad.html

Unfortunately SDL doesn't make use of it currently. So I've took it upon myself to add it; patch is in the attachments.

Basically what the patch does is that if SDL finds no built-it controller mappings for a given joystick it then asks the joystick backend to autodetect it, and that uses the relevant evdev bits to figure out which button/axis is which. (See the specs for more details.)

With this patch applied my own driver for my controller works out-of-box with SDL with no extra configuration and is correctly recognized as a gamepad; this is also going to be the case for any other driver which follows the Linux Gamepad Specification.

src/joystick/SDL_gamecontroller.c

@@ -1089,6 +1089,91 @@ static ControllerMapping_t *SDL_PrivateGetControllerMappingForNameAndGUID(const
     return mapping;
 }
 
+static void SDL_PrivateAppendToMappingString(char *mapping_string,
+                                             size_t mapping_string_len,
+                                             const char *input_name,
+                                             SDL_InputMapping *mapping)
+{
+    char buffer[16];
+    if (mapping->kind == EMappingKind_None) {
+        return;
+    }
+
+    SDL_strlcat(mapping_string, input_name, mapping_string_len);
+    SDL_strlcat(mapping_string, ":", mapping_string_len);
+    switch (mapping->kind) {
+        case EMappingKind_Button:
+            SDL_snprintf(buffer, sizeof(buffer), "b%i", mapping->target);
+            break;
+        case EMappingKind_Axis:
+            SDL_snprintf(buffer, sizeof(buffer), "a%i", mapping->target);
+            break;
+        case EMappingKind_Hat:
+            SDL_snprintf(buffer, sizeof(buffer), "h%i.%i", mapping->target >> 4, mapping->target & 0x0F);
+            break;
+        default:
+            SDL_assert(SDL_FALSE);
+    }
+
+    SDL_strlcat(mapping_string, buffer, mapping_string_len);
+    SDL_strlcat(mapping_string, ",", mapping_string_len);
+}
+
+static ControllerMapping_t *SDL_PrivateGenerateAutomaticControllerMapping(const char *name,
+                                                                          SDL_JoystickGUID guid,
+                                                                          SDL_GamepadMapping *raw_map)
+{
+    SDL_bool existing;
+    char name_string[128];
+    char mapping[1024];
+
+    /* Remove any commas in the name */
+    SDL_strlcpy(name_string, name, sizeof(name_string));
+    {
+        char *spot;
+        for (spot = name_string; *spot; ++spot) {
+            if (*spot == ',') {
+                *spot = ' ';
+            }
+        }
+    }
+    SDL_snprintf(mapping, sizeof(mapping), "none,%s,", name_string);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "a", &raw_map->a);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "b", &raw_map->b);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "x", &raw_map->x);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "y", &raw_map->y);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "back", &raw_map->back);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "guide", &raw_map->guide);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "start", &raw_map->start);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "leftstick", &raw_map->leftstick);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "rightstick", &raw_map->rightstick);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "leftshoulder", &raw_map->leftshoulder);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "rightshoulder", &raw_map->rightshoulder);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "dpup", &raw_map->dpup);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "dpdown", &raw_map->dpdown);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "dpleft", &raw_map->dpleft);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "dpright", &raw_map->dpright);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "leftx", &raw_map->leftx);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "lefty", &raw_map->lefty);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "rightx", &raw_map->rightx);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "righty", &raw_map->righty);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "lefttrigger", &raw_map->lefttrigger);
+    SDL_PrivateAppendToMappingString(mapping, sizeof(mapping), "righttrigger", &raw_map->righttrigger);
+
+    /* Remove trailing comma */
+    {
+        int pos = (int)SDL_strlen(mapping) - 1;
+        if (pos >= 0) {
+            if (mapping[pos] == ',') {
+                mapping[pos] = '\0';
+            }
+        }
+    }
+
+    return SDL_PrivateAddMappingForGUID(guid, mapping,
+                      &existing, SDL_CONTROLLER_MAPPING_PRIORITY_DEFAULT);
+}
+
 static ControllerMapping_t *SDL_PrivateGetControllerMapping(int device_index)
 {
     const char *name;
@@ -1106,6 +1191,13 @@ static ControllerMapping_t *SDL_PrivateGetControllerMapping(int device_index)
     name = SDL_JoystickNameForIndex(device_index);
     guid = SDL_JoystickGetDeviceGUID(device_index);
     mapping = SDL_PrivateGetControllerMappingForNameAndGUID(name, guid);
+    if (!mapping) {
+        SDL_GamepadMapping raw_map;
+        if (SDL_PrivateJoystickGetAutoGamepadMapping(device_index, &raw_map)) {
+            mapping = SDL_PrivateGenerateAutomaticControllerMapping(name, guid, &raw_map);
+        }
+    }
+
     SDL_UnlockJoysticks();
     return mapping;
 }

src/joystick/SDL_joystick.c

@@ -584,6 +584,21 @@ SDL_PrivateJoystickValid(SDL_Joystick * joystick)
     return valid;
 }
 
+SDL_bool
+SDL_PrivateJoystickGetAutoGamepadMapping(int device_index, SDL_GamepadMapping * out)
+{
+    SDL_JoystickDriver *driver;
+    SDL_bool is_ok = SDL_FALSE;
+
+    SDL_LockJoysticks();
+    if (SDL_GetDriverAndJoystickIndex(device_index, &driver, &device_index)) {
+        is_ok = driver->GetGamepadMapping(device_index, out);
+    }
+    SDL_UnlockJoysticks();
+
+    return is_ok;
+}
+
 /*
  * Get the number of multi-dimensional axis controls on a joystick
  */

src/joystick/SDL_joystick_c.h

@@ -111,6 +111,49 @@ extern void SDL_PrivateJoystickBatteryLevel(SDL_Joystick * joystick,
 /* Internal sanity checking functions */
 extern SDL_bool SDL_PrivateJoystickValid(SDL_Joystick * joystick);
 
+typedef enum
+{
+    EMappingKind_None = 0,
+    EMappingKind_Button = 1,
+    EMappingKind_Axis = 2,
+    EMappingKind_Hat = 3
+} EMappingKind;
+
+typedef struct _SDL_InputMapping
+{
+    EMappingKind kind;
+    Uint8 target;
+} SDL_InputMapping;
+
+typedef struct _SDL_GamepadMapping
+{
+    SDL_InputMapping a;
+    SDL_InputMapping b;
+    SDL_InputMapping x;
+    SDL_InputMapping y;
+    SDL_InputMapping back;
+    SDL_InputMapping guide;
+    SDL_InputMapping start;
+    SDL_InputMapping leftstick;
+    SDL_InputMapping rightstick;
+    SDL_InputMapping leftshoulder;
+    SDL_InputMapping rightshoulder;
+    SDL_InputMapping dpup;
+    SDL_InputMapping dpdown;
+    SDL_InputMapping dpleft;
+    SDL_InputMapping dpright;
+    SDL_InputMapping leftx;
+    SDL_InputMapping lefty;
+    SDL_InputMapping rightx;
+    SDL_InputMapping righty;
+    SDL_InputMapping lefttrigger;
+    SDL_InputMapping righttrigger;
+} SDL_GamepadMapping;
+
+/* Function to get autodetected gamepad controller mapping from the driver */
+extern SDL_bool SDL_PrivateJoystickGetAutoGamepadMapping(int device_index,
+                                                         SDL_GamepadMapping *out);
+
 #endif /* SDL_joystick_c_h_ */
 
 /* vi: set ts=4 sw=4 expandtab: */

src/joystick/SDL_sysjoystick.h

@@ -136,6 +136,9 @@ typedef struct _SDL_JoystickDriver
     /* Function to perform any system-specific joystick related cleanup */
     void (*Quit)(void);
 
+    /* Function to get the autodetected controller mapping; returns false if there isn't any. */
+    SDL_bool (*GetGamepadMapping)(int device_index, SDL_GamepadMapping * out);
+
 } SDL_JoystickDriver;
 
 /* Windows and Mac OSX has a limit of MAX_DWORD / 1000, Linux kernel has a limit of 0xFFFF */

src/joystick/android/SDL_sysjoystick.c

@@ -693,6 +693,12 @@ ANDROID_JoystickQuit(void)
 #endif /* 0 */
 }
 
+static SDL_bool
+ANDROID_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_ANDROID_JoystickDriver =
 {
     ANDROID_JoystickInit,
@@ -708,6 +714,7 @@ SDL_JoystickDriver SDL_ANDROID_JoystickDriver =
     ANDROID_JoystickUpdate,
     ANDROID_JoystickClose,
     ANDROID_JoystickQuit,
+    ANDROID_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_ANDROID */

src/joystick/bsd/SDL_sysjoystick.c

@@ -762,6 +762,12 @@ BSD_JoystickRumble(SDL_Joystick * joystick, Uint16 low_frequency_rumble, Uint16
     return SDL_Unsupported();
 }
 
+static SDL_bool
+BSD_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_BSD_JoystickDriver =
 {
     BSD_JoystickInit,
@@ -777,6 +783,7 @@ SDL_JoystickDriver SDL_BSD_JoystickDriver =
     BSD_JoystickUpdate,
     BSD_JoystickClose,
     BSD_JoystickQuit,
+    BSD_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_USBHID */

src/joystick/darwin/SDL_sysjoystick.c

@@ -1051,6 +1051,12 @@ DARWIN_JoystickQuit(void)
     }
 }
 
+static SDL_bool
+DARWIN_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_DARWIN_JoystickDriver =
 {
     DARWIN_JoystickInit,
@@ -1066,6 +1072,7 @@ SDL_JoystickDriver SDL_DARWIN_JoystickDriver =
     DARWIN_JoystickUpdate,
     DARWIN_JoystickClose,
     DARWIN_JoystickQuit,
+    DARWIN_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_IOKIT */

src/joystick/dummy/SDL_sysjoystick.c

@@ -104,6 +104,12 @@ DUMMY_JoystickQuit(void)
 {
 }
 
+static SDL_bool
+DUMMY_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_DUMMY_JoystickDriver =
 {
     DUMMY_JoystickInit,
@@ -119,6 +125,7 @@ SDL_JoystickDriver SDL_DUMMY_JoystickDriver =
     DUMMY_JoystickUpdate,
     DUMMY_JoystickClose,
     DUMMY_JoystickQuit,
+    DUMMY_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_DUMMY || SDL_JOYSTICK_DISABLED */

src/joystick/emscripten/SDL_sysjoystick.c

@@ -403,6 +403,12 @@ EMSCRIPTEN_JoystickRumble(SDL_Joystick * joystick, Uint16 low_frequency_rumble,
     return SDL_Unsupported();
 }
 
+static SDL_bool
+EMSCRIPTEN_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_EMSCRIPTEN_JoystickDriver =
 {
     EMSCRIPTEN_JoystickInit,
@@ -418,6 +424,7 @@ SDL_JoystickDriver SDL_EMSCRIPTEN_JoystickDriver =
     EMSCRIPTEN_JoystickUpdate,
     EMSCRIPTEN_JoystickClose,
     EMSCRIPTEN_JoystickQuit,
+    EMSCRIPTEN_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_EMSCRIPTEN */

src/joystick/haiku/SDL_haikujoystick.cc

@@ -259,6 +259,12 @@ extern "C"
         return SDL_Unsupported();
     }
 
+    static SDL_bool
+    HAIKU_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+    {
+        return SDL_FALSE;
+    }
+
     SDL_JoystickDriver SDL_HAIKU_JoystickDriver =
     {
         HAIKU_JoystickInit,
@@ -274,6 +280,7 @@ extern "C"
         HAIKU_JoystickUpdate,
         HAIKU_JoystickClose,
         HAIKU_JoystickQuit,
+        HAIKU_JoystickGetGamepadMapping
     };
 
 }                              // extern "C"

src/joystick/hidapi/SDL_hidapijoystick.c

@@ -1101,6 +1101,12 @@ HIDAPI_JoystickQuit(void)
     initialized = SDL_FALSE;
 }
 
+static SDL_bool
+HIDAPI_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_HIDAPI_JoystickDriver =
 {
     HIDAPI_JoystickInit,
@@ -1116,6 +1122,7 @@ SDL_JoystickDriver SDL_HIDAPI_JoystickDriver =
     HIDAPI_JoystickUpdate,
     HIDAPI_JoystickClose,
     HIDAPI_JoystickQuit,
+    HIDAPI_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_HIDAPI */

src/joystick/iphoneos/SDL_sysjoystick.m

@@ -850,6 +850,12 @@ IOS_JoystickQuit(void)
     numjoysticks = 0;
 }
 
+static SDL_bool
+IOS_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_IOS_JoystickDriver =
 {
     IOS_JoystickInit,
@@ -865,6 +871,7 @@ SDL_JoystickDriver SDL_IOS_JoystickDriver =
     IOS_JoystickUpdate,
     IOS_JoystickClose,
     IOS_JoystickQuit,
+    IOS_JoystickGetGamepadMapping
 };
 
 /* vi: set ts=4 sw=4 expandtab: */

src/joystick/linux/SDL_sysjoystick.c

@@ -656,6 +656,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
                 printf("Joystick has button: 0x%x\n", i);
 #endif
                 joystick->hwdata->key_map[i] = joystick->nbuttons;
+                joystick->hwdata->has_key[i] = SDL_TRUE;
                 ++joystick->nbuttons;
             }
         }
@@ -665,6 +666,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
                 printf("Joystick has button: 0x%x\n", i);
 #endif
                 joystick->hwdata->key_map[i] = joystick->nbuttons;
+                joystick->hwdata->has_key[i] = SDL_TRUE;
                 ++joystick->nbuttons;
             }
         }
@@ -687,6 +689,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
                        absinfo.fuzz, absinfo.flat);
 #endif /* DEBUG_INPUT_EVENTS */
                 joystick->hwdata->abs_map[i] = joystick->naxes;
+                joystick->hwdata->has_abs[i] = SDL_TRUE;
                 if (absinfo.minimum == absinfo.maximum) {
                     joystick->hwdata->abs_correct[i].used = 0;
                 } else {
@@ -721,6 +724,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
                        absinfo.fuzz, absinfo.flat);
 #endif /* DEBUG_INPUT_EVENTS */
                 joystick->hwdata->hats_indices[hat_index] = joystick->nhats++;
+                joystick->hwdata->has_hat[hat_index] = SDL_TRUE;
             }
         }
         if (test_bit(REL_X, relbit) || test_bit(REL_Y, relbit)) {
@@ -1100,6 +1104,181 @@ LINUX_JoystickQuit(void)
     SDL_QuitSteamControllers();
 }
 
+/*
+   This is based on the Linux Gamepad Specification
+   available at: https://www.kernel.org/doc/html/v4.15/input/gamepad.html
+ */
+static SDL_bool
+LINUX_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    SDL_Joystick * joystick;
+
+    joystick = (SDL_Joystick *) SDL_calloc(sizeof(*joystick), 1);
+    if (joystick == NULL) {
+        SDL_OutOfMemory();
+        return SDL_FALSE;
+    }
+
+    /* We temporarily open the device to check how it's configured. */
+    if (LINUX_JoystickOpen(joystick, device_index) < 0) {
+        SDL_free(joystick);
+        return SDL_FALSE;
+    }
+
+    if (!joystick->hwdata->has_key[BTN_GAMEPAD]) {
+        /* Not a gamepad according to the specs. */
+        LINUX_JoystickClose(joystick);
+        SDL_free(joystick);
+        return SDL_FALSE;
+    }
+
+    /* We have a gamepad; start filling out the mappings. */
+    memset(out, 0, sizeof(SDL_GamepadMapping));
+
+    if (joystick->hwdata->has_key[BTN_SOUTH]) {
+        out->a.kind = EMappingKind_Button;
+        out->a.target = joystick->hwdata->key_map[BTN_SOUTH];
+    }
+
+    if (joystick->hwdata->has_key[BTN_EAST]) {
+        out->b.kind = EMappingKind_Button;
+        out->b.target = joystick->hwdata->key_map[BTN_EAST];
+    }
+
+    if (joystick->hwdata->has_key[BTN_NORTH]) {
+        out->y.kind = EMappingKind_Button;
+        out->y.target = joystick->hwdata->key_map[BTN_NORTH];
+    }
+
+    if (joystick->hwdata->has_key[BTN_WEST]) {
+        out->x.kind = EMappingKind_Button;
+        out->x.target = joystick->hwdata->key_map[BTN_WEST];
+    }
+
+    if (joystick->hwdata->has_key[BTN_SELECT]) {
+        out->back.kind = EMappingKind_Button;
+        out->back.target = joystick->hwdata->key_map[BTN_SELECT];
+    }
+
+    if (joystick->hwdata->has_key[BTN_START]) {
+        out->start.kind = EMappingKind_Button;
+        out->start.target = joystick->hwdata->key_map[BTN_START];
+    }
+
+    if (joystick->hwdata->has_key[BTN_THUMBL]) {
+        out->leftstick.kind = EMappingKind_Button;
+        out->leftstick.target = joystick->hwdata->key_map[BTN_THUMBL];
+    }
+
+    if (joystick->hwdata->has_key[BTN_THUMBR]) {
+        out->rightstick.kind = EMappingKind_Button;
+        out->rightstick.target = joystick->hwdata->key_map[BTN_THUMBR];
+    }
+
+    if (joystick->hwdata->has_key[BTN_MODE]) {
+        out->guide.kind = EMappingKind_Button;
+        out->guide.target = joystick->hwdata->key_map[BTN_MODE];
+    }
+
+    /*
+       According to the specs the D-Pad, the shoulder buttons and the triggers
+       can be digital, or analog, or both at the same time.
+     */
+
+    /* Prefer digital shoulder buttons, but settle for analog if missing. */
+    if (joystick->hwdata->has_key[BTN_TL]) {
+        out->leftshoulder.kind = EMappingKind_Button;
+        out->leftshoulder.target = joystick->hwdata->key_map[BTN_TL];
+    }
+
+    if (joystick->hwdata->has_key[BTN_TR]) {
+        out->rightshoulder.kind = EMappingKind_Button;
+        out->rightshoulder.target = joystick->hwdata->key_map[BTN_TR];
+    }
+
+    if (joystick->hwdata->has_hat[1] && /* Check if ABS_HAT1{X, Y} is available. */
+       (!joystick->hwdata->has_key[BTN_TL] || !joystick->hwdata->has_key[BTN_TR])) {
+        int hat = joystick->hwdata->hats_indices[1] << 4;
+        out->leftshoulder.kind = EMappingKind_Hat;
+        out->rightshoulder.kind = EMappingKind_Hat;
+        out->leftshoulder.target = hat | 0x4;
+        out->rightshoulder.target = hat | 0x2;
+    }
+
+    /* Prefer analog triggers, but settle for digital if missing. */
+    if (joystick->hwdata->has_hat[2]) { /* Check if ABS_HAT2{X,Y} is available. */
+        int hat = joystick->hwdata->hats_indices[2] << 4;
+        out->lefttrigger.kind = EMappingKind_Hat;
+        out->righttrigger.kind = EMappingKind_Hat;
+        out->lefttrigger.target = hat | 0x4;
+        out->righttrigger.target = hat | 0x2;
+    } else {
+        if (joystick->hwdata->has_key[BTN_TL2]) {
+            out->lefttrigger.kind = EMappingKind_Button;
+            out->lefttrigger.target = joystick->hwdata->key_map[BTN_TL2];
+        }
+
+        if (joystick->hwdata->has_key[BTN_TR2]) {
+            out->righttrigger.kind = EMappingKind_Button;
+            out->righttrigger.target = joystick->hwdata->key_map[BTN_TR2];
+        }
+    }
+
+    /* Prefer digital D-Pad, but settle for analog if missing. */
+    if (joystick->hwdata->has_key[BTN_DPAD_UP]) {
+        out->dpup.kind = EMappingKind_Button;
+        out->dpup.target = joystick->hwdata->key_map[BTN_DPAD_UP];
+    }
+
+    if (joystick->hwdata->has_key[BTN_DPAD_DOWN]) {
+        out->dpdown.kind = EMappingKind_Button;
+        out->dpdown.target = joystick->hwdata->key_map[BTN_DPAD_DOWN];
+    }
+
+    if (joystick->hwdata->has_key[BTN_DPAD_LEFT]) {
+        out->dpleft.kind = EMappingKind_Button;
+        out->dpleft.target = joystick->hwdata->key_map[BTN_DPAD_LEFT];
+    }
+
+    if (joystick->hwdata->has_key[BTN_DPAD_RIGHT]) {
+        out->dpright.kind = EMappingKind_Button;
+        out->dpright.target = joystick->hwdata->key_map[BTN_DPAD_RIGHT];
+    }
+
+    if (joystick->hwdata->has_hat[0] && /* Check if ABS_HAT0{X,Y} is available. */
+       (!joystick->hwdata->has_key[BTN_DPAD_LEFT] || !joystick->hwdata->has_key[BTN_DPAD_RIGHT] ||
+        !joystick->hwdata->has_key[BTN_DPAD_UP] || !joystick->hwdata->has_key[BTN_DPAD_DOWN])) {
+       int hat = joystick->hwdata->hats_indices[0] << 4;
+       out->dpleft.kind = EMappingKind_Hat;
+       out->dpright.kind = EMappingKind_Hat;
+       out->dpup.kind = EMappingKind_Hat;
+       out->dpdown.kind = EMappingKind_Hat;
+       out->dpleft.target = hat | 0x8;
+       out->dpright.target = hat | 0x2;
+       out->dpup.target = hat | 0x1;
+       out->dpdown.target = hat | 0x4;
+    }
+
+    if (joystick->hwdata->has_abs[ABS_X] && joystick->hwdata->has_abs[ABS_Y]) {
+        out->leftx.kind = EMappingKind_Axis;
+        out->lefty.kind = EMappingKind_Axis;
+        out->leftx.target = joystick->hwdata->abs_map[ABS_X];
+        out->lefty.target = joystick->hwdata->abs_map[ABS_Y];
+    }
+
+    if (joystick->hwdata->has_abs[ABS_RX] && joystick->hwdata->has_abs[ABS_RY]) {
+        out->rightx.kind = EMappingKind_Axis;
+        out->righty.kind = EMappingKind_Axis;
+        out->rightx.target = joystick->hwdata->abs_map[ABS_RX];
+        out->righty.target = joystick->hwdata->abs_map[ABS_RY];
+    }
+
+    LINUX_JoystickClose(joystick);
+    SDL_free(joystick);
+
+    return SDL_TRUE;
+}
+
 SDL_JoystickDriver SDL_LINUX_JoystickDriver =
 {
     LINUX_JoystickInit,
@@ -1115,6 +1294,7 @@ SDL_JoystickDriver SDL_LINUX_JoystickDriver =
     LINUX_JoystickUpdate,
     LINUX_JoystickClose,
     LINUX_JoystickQuit,
+    LINUX_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_LINUX */

src/joystick/linux/SDL_sysjoystick_c.h

@@ -53,6 +53,9 @@ struct joystick_hwdata
     /* Support for the Linux 2.4 unified input interface */
     Uint8 key_map[KEY_MAX];
     Uint8 abs_map[ABS_MAX];
+    SDL_bool has_key[KEY_MAX];
+    SDL_bool has_abs[ABS_MAX];
+
     struct axis_correct
     {
         int used;
@@ -65,6 +68,7 @@ struct joystick_hwdata
     SDL_bool m_bSteamController;
     /* 4 = (ABS_HAT3X-ABS_HAT0X)/2 (see input-event-codes.h in kernel) */
     int hats_indices[4];
+    SDL_bool has_hat[4];
 
     /* Set when gamepad is pending removal due to ENODEV read error */
     SDL_bool gone;

src/joystick/virtual/SDL_virtualjoystick.c

@@ -391,6 +391,11 @@ VIRTUAL_JoystickQuit(void)
     }
 }
 
+static SDL_bool
+VIRTUAL_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
 
 SDL_JoystickDriver SDL_VIRTUAL_JoystickDriver =
 {
@@ -407,6 +412,7 @@ SDL_JoystickDriver SDL_VIRTUAL_JoystickDriver =
     VIRTUAL_JoystickUpdate,
     VIRTUAL_JoystickClose,
     VIRTUAL_JoystickQuit,
+    VIRTUAL_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_VIRTUAL || SDL_JOYSTICK_DISABLED */

src/joystick/windows/SDL_rawinputjoystick.c

@@ -725,6 +725,11 @@ RAWINPUT_JoystickQuit(void)
     SDL_RAWINPUT_inited = SDL_FALSE;
 }
 
+static SDL_bool
+RAWINPUT_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
 
 SDL_JoystickDriver SDL_RAWINPUT_JoystickDriver =
 {
@@ -741,6 +746,7 @@ SDL_JoystickDriver SDL_RAWINPUT_JoystickDriver =
     RAWINPUT_JoystickUpdate,
     RAWINPUT_JoystickClose,
     RAWINPUT_JoystickQuit,
+    RAWINPUT_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_RAWINPUT */

src/joystick/windows/SDL_windows_gaming_input.c

@@ -699,6 +699,12 @@ WGI_JoystickQuit(void)
     WIN_CoUninitialize();
 }
 
+static SDL_bool
+WGI_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_WGI_JoystickDriver =
 {
     WGI_JoystickInit,
@@ -714,6 +720,7 @@ SDL_JoystickDriver SDL_WGI_JoystickDriver =
     WGI_JoystickUpdate,
     WGI_JoystickClose,
     WGI_JoystickQuit,
+    WGI_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_WGI */

src/joystick/windows/SDL_windowsjoystick.c

@@ -555,6 +555,12 @@ WINDOWS_JoystickQuit(void)
     s_bDeviceRemoved = SDL_FALSE;
 }
 
+static SDL_bool
+WINDOWS_JoystickGetGamepadMapping(int device_index, SDL_GamepadMapping *out)
+{
+    return SDL_FALSE;
+}
+
 SDL_JoystickDriver SDL_WINDOWS_JoystickDriver =
 {
     WINDOWS_JoystickInit,
@@ -570,6 +576,7 @@ SDL_JoystickDriver SDL_WINDOWS_JoystickDriver =
     WINDOWS_JoystickUpdate,
     WINDOWS_JoystickClose,
     WINDOWS_JoystickQuit,
+    WINDOWS_JoystickGetGamepadMapping
 };
 
 #endif /* SDL_JOYSTICK_DINPUT || SDL_JOYSTICK_XINPUT */