STEAMOS: Dynamic swapchain override for gamescope limiter

src/gallium/frontends/dri/loader_dri3_helper.c

@@ -274,6 +274,30 @@ dri3_update_max_num_back(struct loader_dri3_drawable *draw)
    }
 }
 
+static unsigned
+gamescope_swapchain_override()
+{
+   const char *path = getenv("GAMESCOPE_LIMITER_FILE");
+   if (!path)
+      return 0;
+
+   static simple_mtx_t mtx = SIMPLE_MTX_INITIALIZER;
+   static int fd = -1;
+
+   simple_mtx_lock(&mtx);
+   if (fd < 0) {
+      fd = open(path, O_RDONLY);
+   }
+   simple_mtx_unlock(&mtx);
+
+   if (fd < 0)
+      return 0;
+
+   uint32_t override_value = 0;
+   pread(fd, &override_value, sizeof(override_value), 0);
+   return override_value;
+}
+
 void
 loader_dri3_set_swap_interval(struct loader_dri3_drawable *draw, int interval)
 {
@@ -288,10 +312,12 @@ loader_dri3_set_swap_interval(struct loader_dri3_drawable *draw, int interval)
     * PS. changing from value A to B and A < B won't cause swap out of order but
     * may still gets wrong target_msc value at the beginning.
     */
-   if (draw->swap_interval != interval)
+   if (draw->orig_swap_interval != interval)
       loader_dri3_swapbuffer_barrier(draw);
 
-   draw->swap_interval = interval;
+   draw->orig_swap_interval = interval;
+   if (gamescope_swapchain_override() != 1)
+      draw->swap_interval = interval;
 }
 
 static void
@@ -419,6 +445,11 @@ loader_dri3_drawable_init(xcb_connection_t *conn,
       set_adaptive_sync_property(conn, draw->drawable, false);
 
    draw->swap_interval = dri_get_initial_swap_interval(draw->dri_screen_render_gpu);
+   draw->orig_swap_interval = draw->swap_interval;
+
+   unsigned gamescope_override = gamescope_swapchain_override();
+   if (gamescope_override == 1)
+      draw->swap_interval = 1;
 
    dri3_update_max_num_back(draw);
 
@@ -1064,6 +1095,12 @@ loader_dri3_swap_buffers_msc(struct loader_dri3_drawable *draw,
    if (draw->type == LOADER_DRI3_DRAWABLE_WINDOW) {
       dri3_fence_reset(draw->conn, back);
 
+      unsigned gamescope_override = gamescope_swapchain_override();
+      if (gamescope_override == 1)
+         draw->swap_interval = 1;
+      else
+         draw->swap_interval = draw->orig_swap_interval;
+
       /* Compute when we want the frame shown by taking the last known
        * successful MSC and adding in a swap interval for each outstanding swap
        * request. target_msc=divisor=remainder=0 means "Use glXSwapBuffers()

src/gallium/frontends/dri/loader_dri3_helper.h

@@ -170,6 +170,7 @@ struct loader_dri3_drawable {
    bool block_on_depleted_buffers;
    bool queries_buffer_age;
    int swap_interval;
+   int orig_swap_interval;
 
    const struct loader_dri3_vtable *vtable;
 

src/vulkan/wsi/wsi_common_x11.c

@@ -49,6 +49,7 @@
 #include "util/mesa-blake3.h"
 #include "util/os_file.h"
 #include "util/os_time.h"
+#include "util/simple_mtx.h"
 #include "util/u_debug.h"
 #include "util/u_thread.h"
 #include "util/xmlconfig.h"
@@ -223,6 +224,30 @@ wsi_x11_detect_xwayland(xcb_connection_t *conn,
    return is_xwayland;
 }
 
+static unsigned
+gamescope_swapchain_override()
+{
+   const char *path = getenv("GAMESCOPE_LIMITER_FILE");
+   if (!path)
+      return 0;
+
+   static simple_mtx_t mtx = SIMPLE_MTX_INITIALIZER;
+   static int fd = -1;
+
+   simple_mtx_lock(&mtx);
+   if (fd < 0) {
+      fd = open(path, O_RDONLY);
+   }
+   simple_mtx_unlock(&mtx);
+
+   if (fd < 0)
+      return 0;
+
+   uint32_t override_value = 0;
+   pread(fd, &override_value, sizeof(override_value), 0);
+   return override_value;
+}
+
 static struct wsi_x11_connection *
 wsi_x11_connection_create(struct wsi_device *wsi_dev,
                           xcb_connection_t *conn)
@@ -1128,6 +1153,8 @@ struct x11_swapchain {
    uint64_t                                     present_id;
    VkResult                                     present_progress_error;
 
+   VkPresentModeKHR                             orig_present_mode;
+
    struct x11_image                             images[0];
 };
 VK_DEFINE_NONDISP_HANDLE_CASTS(x11_swapchain, base.base, VkSwapchainKHR,
@@ -1805,6 +1832,12 @@ x11_queue_present(struct wsi_swapchain *anv_chain,
    if (status < 0)
       return status;
 
+   unsigned gamescope_override = gamescope_swapchain_override();
+   if ((gamescope_override == 1 && chain->base.present_mode != VK_PRESENT_MODE_FIFO_KHR) ||
+       (gamescope_override != 1 && chain->base.present_mode != chain->orig_present_mode)) {
+      return x11_swapchain_result(chain, VK_ERROR_OUT_OF_DATE_KHR);
+   }
+
    if (damage && damage->pRectangles && damage->rectangleCount > 0 &&
       damage->rectangleCount <= MAX_DAMAGE_RECTS) {
       xcb_rectangle_t *rects = chain->images[image_index].rects;
@@ -2524,6 +2557,10 @@ x11_surface_create_swapchain(VkIcdSurfaceBase *icd_surface,
    xcb_void_cookie_t cookie;
    VkResult result;
    VkPresentModeKHR present_mode = wsi_swapchain_get_present_mode(wsi_device, pCreateInfo);
+   VkPresentModeKHR orig_present_mode = present_mode;
+
+   if (gamescope_swapchain_override() == 1)
+      present_mode = VK_PRESENT_MODE_FIFO_KHR;
 
    assert(pCreateInfo->sType == VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR);
 
@@ -2675,6 +2712,7 @@ x11_surface_create_swapchain(VkIcdSurfaceBase *icd_surface,
    chain->base.release_images = x11_release_images;
    chain->base.set_present_mode = x11_set_present_mode;
    chain->base.present_mode = present_mode;
+   chain->orig_present_mode = orig_present_mode;
    chain->base.image_count = num_images;
    chain->conn = conn;
    chain->window = window;