minui/graphics_drm.cpp - android_bootable_recovery - Gitiles

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "graphics_drm.h"

 #include <fcntl.h>
 #include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <drm_fourcc.h>
 #include <xf86drm.h>
 #include <xf86drmMode.h>

 #include "minui/minui.h"

 #define ARRAY_SIZE(A) (sizeof(A)/sizeof(*(A)))

 MinuiBackendDrm::MinuiBackendDrm()
     : GRSurfaceDrms(), main_monitor_crtc(nullptr), main_monitor_connector(nullptr), drm_fd(-1) {}

 void MinuiBackendDrm::DrmDisableCrtc(int drm_fd, drmModeCrtc* crtc) {
   if (crtc) {
     drmModeSetCrtc(drm_fd, crtc->crtc_id,
                    0,         // fb_id
                    0, 0,      // x,y
                    nullptr,   // connectors
                    0,         // connector_count
                    nullptr);  // mode
   }
 }

 int MinuiBackendDrm::DrmEnableCrtc(int drm_fd, drmModeCrtc* crtc, GRSurfaceDrm* surface) {
   int ret = drmModeSetCrtc(drm_fd, crtc->crtc_id, surface->fb_id, 0, 0,  // x,y
                            &main_monitor_connector->connector_id,
                            1,  // connector_count
                            &main_monitor_crtc->mode);

   if (ret) {
     printf("drmModeSetCrtc failed ret=%d\n", ret);
   }

   return ret;
 }

 void MinuiBackendDrm::Blank(bool blank) {
   if (blank) {
     DrmDisableCrtc(drm_fd, main_monitor_crtc);
   } else {
     DrmEnableCrtc(drm_fd, main_monitor_crtc, GRSurfaceDrms[current_buffer]);
   }
 }

 void MinuiBackendDrm::DrmDestroySurface(GRSurfaceDrm* surface) {
   if (!surface) return;

   if (surface->data) {
     munmap(surface->data, surface->row_bytes * surface->height);
   }

   if (surface->fb_id) {
     int ret = drmModeRmFB(drm_fd, surface->fb_id);
     if (ret) {
       printf("drmModeRmFB failed ret=%d\n", ret);
     }
   }

   if (surface->handle) {
     drm_gem_close gem_close = {};
     gem_close.handle = surface->handle;

     int ret = drmIoctl(drm_fd, DRM_IOCTL_GEM_CLOSE, &gem_close);
     if (ret) {
       printf("DRM_IOCTL_GEM_CLOSE failed ret=%d\n", ret);
     }
   }

   delete surface;
 }

 static int drm_format_to_bpp(uint32_t format) {
   switch (format) {
     case DRM_FORMAT_ABGR8888:
     case DRM_FORMAT_BGRA8888:
     case DRM_FORMAT_RGBX8888:
     case DRM_FORMAT_BGRX8888:
     case DRM_FORMAT_XBGR8888:
     case DRM_FORMAT_XRGB8888:
       return 32;
     case DRM_FORMAT_RGB565:
       return 16;
     default:
       printf("Unknown format %d\n", format);
       return 32;
   }
 }

 GRSurfaceDrm* MinuiBackendDrm::DrmCreateSurface(int width, int height) {
   GRSurfaceDrm* surface = new GRSurfaceDrm;
   *surface = {};

   uint32_t format;
   PixelFormat pixel_format = gr_pixel_format();
   // PixelFormat comes in byte order, whereas DRM_FORMAT_* uses little-endian
   // (external/libdrm/include/drm/drm_fourcc.h). Note that although drm_fourcc.h also defines a
   // macro of DRM_FORMAT_BIG_ENDIAN, it doesn't seem to be actually supported (see the discussion
   // in https://lists.freedesktop.org/archives/amd-gfx/2017-May/008560.html).
   if (pixel_format == PixelFormat::ABGR) {
     format = DRM_FORMAT_RGBA8888;
   } else if (pixel_format == PixelFormat::BGRA) {
     format = DRM_FORMAT_ARGB8888;
   } else if (pixel_format == PixelFormat::RGBX) {
     format = DRM_FORMAT_XBGR8888;
   } else {
     format = DRM_FORMAT_RGB565;
   }

   drm_mode_create_dumb create_dumb = {};
   create_dumb.height = height;
   create_dumb.width = width;
   create_dumb.bpp = drm_format_to_bpp(format);
   create_dumb.flags = 0;

   int ret = drmIoctl(drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb);
   if (ret) {
     printf("DRM_IOCTL_MODE_CREATE_DUMB failed ret=%d\n", ret);
     DrmDestroySurface(surface);
     return nullptr;
   }
   surface->handle = create_dumb.handle;

   uint32_t handles[4], pitches[4], offsets[4];

   handles[0] = surface->handle;
   pitches[0] = create_dumb.pitch;
   offsets[0] = 0;

   ret =
       drmModeAddFB2(drm_fd, width, height, format, handles, pitches, offsets, &(surface->fb_id), 0);
   if (ret) {
     printf("drmModeAddFB2 failed ret=%d\n", ret);
     DrmDestroySurface(surface);
     return nullptr;
   }

   drm_mode_map_dumb map_dumb = {};
   map_dumb.handle = create_dumb.handle;
   ret = drmIoctl(drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb);
   if (ret) {
     printf("DRM_IOCTL_MODE_MAP_DUMB failed ret=%d\n", ret);
     DrmDestroySurface(surface);
     return nullptr;
   }

   surface->height = height;
   surface->width = width;
   surface->row_bytes = create_dumb.pitch;
   surface->pixel_bytes = create_dumb.bpp / 8;
   surface->data = static_cast<unsigned char*>(mmap(nullptr, surface->height * surface->row_bytes,
                                                    PROT_READ | PROT_WRITE, MAP_SHARED, drm_fd,
                                                    map_dumb.offset));
   if (surface->data == MAP_FAILED) {
     perror("mmap() failed");
     DrmDestroySurface(surface);
     return nullptr;
   }

   return surface;
 }

 static drmModeCrtc* find_crtc_for_connector(int fd, drmModeRes* resources,
                                             drmModeConnector* connector) {
   // Find the encoder. If we already have one, just use it.
   drmModeEncoder* encoder;
   if (connector->encoder_id) {
     encoder = drmModeGetEncoder(fd, connector->encoder_id);
   } else {
     encoder = nullptr;
   }

   int32_t crtc;
   if (encoder && encoder->crtc_id) {
     crtc = encoder->crtc_id;
     drmModeFreeEncoder(encoder);
     return drmModeGetCrtc(fd, crtc);
   }

   // Didn't find anything, try to find a crtc and encoder combo.
   crtc = -1;
   for (int i = 0; i < connector->count_encoders; i++) {
     encoder = drmModeGetEncoder(fd, connector->encoders[i]);

     if (encoder) {
       for (int j = 0; j < resources->count_crtcs; j++) {
         if (!(encoder->possible_crtcs & (1 << j))) continue;
         crtc = resources->crtcs[j];
         break;
       }
       if (crtc >= 0) {
         drmModeFreeEncoder(encoder);
         return drmModeGetCrtc(fd, crtc);
       }
     }
   }

   return nullptr;
 }

 static drmModeConnector* find_used_connector_by_type(int fd, drmModeRes* resources, unsigned type) {
   for (int i = 0; i < resources->count_connectors; i++) {
     drmModeConnector* connector = drmModeGetConnector(fd, resources->connectors[i]);
     if (connector) {
       if ((connector->connector_type == type) && (connector->connection == DRM_MODE_CONNECTED) &&
           (connector->count_modes > 0)) {
         return connector;
       }
       drmModeFreeConnector(connector);
     }
   }
   return nullptr;
 }

 static drmModeConnector* find_first_connected_connector(int fd, drmModeRes* resources) {
   for (int i = 0; i < resources->count_connectors; i++) {
     drmModeConnector* connector;

     connector = drmModeGetConnector(fd, resources->connectors[i]);
     if (connector) {
       if ((connector->count_modes > 0) && (connector->connection == DRM_MODE_CONNECTED))
         return connector;

       drmModeFreeConnector(connector);
     }
   }
   return nullptr;
 }

 drmModeConnector* MinuiBackendDrm::FindMainMonitor(int fd, drmModeRes* resources,
                                                    uint32_t* mode_index) {
   /* Look for LVDS/eDP/DSI connectors. Those are the main screens. */
   static constexpr unsigned kConnectorPriority[] = {
     DRM_MODE_CONNECTOR_LVDS,
     DRM_MODE_CONNECTOR_eDP,
     DRM_MODE_CONNECTOR_DSI,
   };

   drmModeConnector* main_monitor_connector = nullptr;
   unsigned i = 0;
   do {
     main_monitor_connector = find_used_connector_by_type(fd, resources, kConnectorPriority[i]);
     i++;
   } while (!main_monitor_connector && i < ARRAY_SIZE(kConnectorPriority));

   /* If we didn't find a connector, grab the first one that is connected. */
   if (!main_monitor_connector) {
     main_monitor_connector = find_first_connected_connector(fd, resources);
   }

   /* If we still didn't find a connector, give up and return. */
   if (!main_monitor_connector) return nullptr;

   *mode_index = 0;
   for (int modes = 0; modes < main_monitor_connector->count_modes; modes++) {
     if (main_monitor_connector->modes[modes].type & DRM_MODE_TYPE_PREFERRED) {
       *mode_index = modes;
       break;
     }
   }

   return main_monitor_connector;
 }

 void MinuiBackendDrm::DisableNonMainCrtcs(int fd, drmModeRes* resources, drmModeCrtc* main_crtc) {
   for (int i = 0; i < resources->count_connectors; i++) {
     drmModeConnector* connector = drmModeGetConnector(fd, resources->connectors[i]);
     drmModeCrtc* crtc = find_crtc_for_connector(fd, resources, connector);
     if (crtc->crtc_id != main_crtc->crtc_id) {
       DrmDisableCrtc(fd, crtc);
     }
     drmModeFreeCrtc(crtc);
   }
 }

 GRSurface* MinuiBackendDrm::Init() {
   drmModeRes* res = nullptr;

   /* Consider DRM devices in order. */
   for (int i = 0; i < DRM_MAX_MINOR; i++) {
     char* dev_name;
     int ret = asprintf(&dev_name, DRM_DEV_NAME, DRM_DIR_NAME, i);
     if (ret < 0) continue;

     drm_fd = open(dev_name, O_RDWR, 0);
     free(dev_name);
     if (drm_fd < 0) continue;

     uint64_t cap = 0;
     /* We need dumb buffers. */
     ret = drmGetCap(drm_fd, DRM_CAP_DUMB_BUFFER, &cap);
     if (ret || cap == 0) {
       close(drm_fd);
       continue;
     }

     res = drmModeGetResources(drm_fd);
     if (!res) {
       close(drm_fd);
       continue;
     }

     /* Use this device if it has at least one connected monitor. */
     if (res->count_crtcs > 0 && res->count_connectors > 0) {
       if (find_first_connected_connector(drm_fd, res)) break;
     }

     drmModeFreeResources(res);
     close(drm_fd);
     res = nullptr;
   }

   if (drm_fd < 0 || res == nullptr) {
     perror("cannot find/open a drm device");
     return nullptr;
   }

   uint32_t selected_mode;
   main_monitor_connector = FindMainMonitor(drm_fd, res, &selected_mode);

   if (!main_monitor_connector) {
     printf("main_monitor_connector not found\n");
     drmModeFreeResources(res);
     close(drm_fd);
     return nullptr;
   }

   main_monitor_crtc = find_crtc_for_connector(drm_fd, res, main_monitor_connector);

   if (!main_monitor_crtc) {
     printf("main_monitor_crtc not found\n");
     drmModeFreeResources(res);
     close(drm_fd);
     return nullptr;
   }

   DisableNonMainCrtcs(drm_fd, res, main_monitor_crtc);

   main_monitor_crtc->mode = main_monitor_connector->modes[selected_mode];

   int width = main_monitor_crtc->mode.hdisplay;
   int height = main_monitor_crtc->mode.vdisplay;

   drmModeFreeResources(res);

   GRSurfaceDrms[0] = DrmCreateSurface(width, height);
   GRSurfaceDrms[1] = DrmCreateSurface(width, height);
   if (!GRSurfaceDrms[0] || !GRSurfaceDrms[1]) {
     // GRSurfaceDrms and drm_fd should be freed in d'tor.
     return nullptr;
   }

   current_buffer = 0;

   // We will likely encounter errors in the backend functions (i.e. Flip) if EnableCrtc fails.
   if (DrmEnableCrtc(drm_fd, main_monitor_crtc, GRSurfaceDrms[1]) != 0) {
     return nullptr;
   }

   return GRSurfaceDrms[0];
 }

 static void page_flip_complete(__unused int fd,
                                __unused unsigned int sequence,
                                __unused unsigned int tv_sec,
                                __unused unsigned int tv_usec,
                                void *user_data) {
   *static_cast<bool*>(user_data) = false;
 }

 GRSurface* MinuiBackendDrm::Flip() {
   bool ongoing_flip = true;

   int ret = drmModePageFlip(drm_fd, main_monitor_crtc->crtc_id,
                             GRSurfaceDrms[current_buffer]->fb_id,
                             DRM_MODE_PAGE_FLIP_EVENT, &ongoing_flip);
   if (ret < 0) {
     printf("drmModePageFlip failed ret=%d\n", ret);
     return nullptr;
   }

   while (ongoing_flip) {
     struct pollfd fds = {
       .fd = drm_fd,
       .events = POLLIN
     };

     ret = poll(&fds, 1, -1);
     if (ret == -1 || !(fds.revents & POLLIN)) {
       printf("poll() failed on drm fd\n");
       break;
     }

     drmEventContext evctx = {
       .version = DRM_EVENT_CONTEXT_VERSION,
       .page_flip_handler = page_flip_complete
     };

     ret = drmHandleEvent(drm_fd, &evctx);
     if (ret != 0) {
       printf("drmHandleEvent failed ret=%d\n", ret);
       break;
     }
   }

   current_buffer = 1 - current_buffer;
   return GRSurfaceDrms[current_buffer];
 }

 MinuiBackendDrm::~MinuiBackendDrm() {
   DrmDisableCrtc(drm_fd, main_monitor_crtc);
   DrmDestroySurface(GRSurfaceDrms[0]);
   DrmDestroySurface(GRSurfaceDrms[1]);
   drmModeFreeCrtc(main_monitor_crtc);
   drmModeFreeConnector(main_monitor_connector);
   close(drm_fd);
   drm_fd = -1;
 }
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "graphics_drm.h"

	#include <fcntl.h>
	#include <poll.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/mman.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <drm_fourcc.h>
	#include <xf86drm.h>
	#include <xf86drmMode.h>

	#include "minui/minui.h"

	#define ARRAY_SIZE(A) (sizeof(A)/sizeof(*(A)))

	MinuiBackendDrm::MinuiBackendDrm()
	: GRSurfaceDrms(), main_monitor_crtc(nullptr), main_monitor_connector(nullptr), drm_fd(-1) {}

	void MinuiBackendDrm::DrmDisableCrtc(int drm_fd, drmModeCrtc* crtc) {
	if (crtc) {
	drmModeSetCrtc(drm_fd, crtc->crtc_id,
	0, // fb_id
	0, 0, // x,y
	nullptr, // connectors
	0, // connector_count
	nullptr); // mode
	}
	}

	int MinuiBackendDrm::DrmEnableCrtc(int drm_fd, drmModeCrtc* crtc, GRSurfaceDrm* surface) {
	int ret = drmModeSetCrtc(drm_fd, crtc->crtc_id, surface->fb_id, 0, 0, // x,y
	&main_monitor_connector->connector_id,
	1, // connector_count
	&main_monitor_crtc->mode);

	if (ret) {
	printf("drmModeSetCrtc failed ret=%d\n", ret);
	}

	return ret;
	}

	void MinuiBackendDrm::Blank(bool blank) {
	if (blank) {
	DrmDisableCrtc(drm_fd, main_monitor_crtc);
	} else {
	DrmEnableCrtc(drm_fd, main_monitor_crtc, GRSurfaceDrms[current_buffer]);
	}
	}

	void MinuiBackendDrm::DrmDestroySurface(GRSurfaceDrm* surface) {
	if (!surface) return;

	if (surface->data) {
	munmap(surface->data, surface->row_bytes * surface->height);
	}

	if (surface->fb_id) {
	int ret = drmModeRmFB(drm_fd, surface->fb_id);
	if (ret) {
	printf("drmModeRmFB failed ret=%d\n", ret);
	}
	}

	if (surface->handle) {
	drm_gem_close gem_close = {};
	gem_close.handle = surface->handle;

	int ret = drmIoctl(drm_fd, DRM_IOCTL_GEM_CLOSE, &gem_close);
	if (ret) {
	printf("DRM_IOCTL_GEM_CLOSE failed ret=%d\n", ret);
	}
	}

	delete surface;
	}

	static int drm_format_to_bpp(uint32_t format) {
	switch (format) {
	case DRM_FORMAT_ABGR8888:
	case DRM_FORMAT_BGRA8888:
	case DRM_FORMAT_RGBX8888:
	case DRM_FORMAT_BGRX8888:
	case DRM_FORMAT_XBGR8888:
	case DRM_FORMAT_XRGB8888:
	return 32;
	case DRM_FORMAT_RGB565:
	return 16;
	default:
	printf("Unknown format %d\n", format);
	return 32;
	}
	}

	GRSurfaceDrm* MinuiBackendDrm::DrmCreateSurface(int width, int height) {
	GRSurfaceDrm* surface = new GRSurfaceDrm;
	*surface = {};

	uint32_t format;
	PixelFormat pixel_format = gr_pixel_format();
	// PixelFormat comes in byte order, whereas DRM_FORMAT_* uses little-endian
	// (external/libdrm/include/drm/drm_fourcc.h). Note that although drm_fourcc.h also defines a
	// macro of DRM_FORMAT_BIG_ENDIAN, it doesn't seem to be actually supported (see the discussion
	// in https://lists.freedesktop.org/archives/amd-gfx/2017-May/008560.html).
	if (pixel_format == PixelFormat::ABGR) {
	format = DRM_FORMAT_RGBA8888;
	} else if (pixel_format == PixelFormat::BGRA) {
	format = DRM_FORMAT_ARGB8888;
	} else if (pixel_format == PixelFormat::RGBX) {
	format = DRM_FORMAT_XBGR8888;
	} else {
	format = DRM_FORMAT_RGB565;
	}

	drm_mode_create_dumb create_dumb = {};
	create_dumb.height = height;
	create_dumb.width = width;
	create_dumb.bpp = drm_format_to_bpp(format);
	create_dumb.flags = 0;

	int ret = drmIoctl(drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb);
	if (ret) {
	printf("DRM_IOCTL_MODE_CREATE_DUMB failed ret=%d\n", ret);
	DrmDestroySurface(surface);
	return nullptr;
	}
	surface->handle = create_dumb.handle;

	uint32_t handles[4], pitches[4], offsets[4];

	handles[0] = surface->handle;
	pitches[0] = create_dumb.pitch;
	offsets[0] = 0;

	ret =
	drmModeAddFB2(drm_fd, width, height, format, handles, pitches, offsets, &(surface->fb_id), 0);
	if (ret) {
	printf("drmModeAddFB2 failed ret=%d\n", ret);
	DrmDestroySurface(surface);
	return nullptr;
	}

	drm_mode_map_dumb map_dumb = {};
	map_dumb.handle = create_dumb.handle;
	ret = drmIoctl(drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb);
	if (ret) {
	printf("DRM_IOCTL_MODE_MAP_DUMB failed ret=%d\n", ret);
	DrmDestroySurface(surface);
	return nullptr;
	}

	surface->height = height;
	surface->width = width;
	surface->row_bytes = create_dumb.pitch;
	surface->pixel_bytes = create_dumb.bpp / 8;
	surface->data = static_cast<unsigned char>(mmap(nullptr, surface->height surface->row_bytes,
	PROT_READ \| PROT_WRITE, MAP_SHARED, drm_fd,
	map_dumb.offset));
	if (surface->data == MAP_FAILED) {
	perror("mmap() failed");
	DrmDestroySurface(surface);
	return nullptr;
	}

	return surface;
	}

	static drmModeCrtc* find_crtc_for_connector(int fd, drmModeRes* resources,
	drmModeConnector* connector) {
	// Find the encoder. If we already have one, just use it.
	drmModeEncoder* encoder;
	if (connector->encoder_id) {
	encoder = drmModeGetEncoder(fd, connector->encoder_id);
	} else {
	encoder = nullptr;
	}

	int32_t crtc;
	if (encoder && encoder->crtc_id) {
	crtc = encoder->crtc_id;
	drmModeFreeEncoder(encoder);
	return drmModeGetCrtc(fd, crtc);
	}

	// Didn't find anything, try to find a crtc and encoder combo.
	crtc = -1;
	for (int i = 0; i < connector->count_encoders; i++) {
	encoder = drmModeGetEncoder(fd, connector->encoders[i]);

	if (encoder) {
	for (int j = 0; j < resources->count_crtcs; j++) {
	if (!(encoder->possible_crtcs & (1 << j))) continue;
	crtc = resources->crtcs[j];
	break;
	}
	if (crtc >= 0) {
	drmModeFreeEncoder(encoder);
	return drmModeGetCrtc(fd, crtc);
	}
	}
	}

	return nullptr;
	}

	static drmModeConnector* find_used_connector_by_type(int fd, drmModeRes* resources, unsigned type) {
	for (int i = 0; i < resources->count_connectors; i++) {
	drmModeConnector* connector = drmModeGetConnector(fd, resources->connectors[i]);
	if (connector) {
	if ((connector->connector_type == type) && (connector->connection == DRM_MODE_CONNECTED) &&
	(connector->count_modes > 0)) {
	return connector;
	}
	drmModeFreeConnector(connector);
	}
	}
	return nullptr;
	}

	static drmModeConnector* find_first_connected_connector(int fd, drmModeRes* resources) {
	for (int i = 0; i < resources->count_connectors; i++) {
	drmModeConnector* connector;

	connector = drmModeGetConnector(fd, resources->connectors[i]);
	if (connector) {
	if ((connector->count_modes > 0) && (connector->connection == DRM_MODE_CONNECTED))
	return connector;

	drmModeFreeConnector(connector);
	}
	}
	return nullptr;
	}

	drmModeConnector* MinuiBackendDrm::FindMainMonitor(int fd, drmModeRes* resources,
	uint32_t* mode_index) {
	/* Look for LVDS/eDP/DSI connectors. Those are the main screens. */
	static constexpr unsigned kConnectorPriority[] = {
	DRM_MODE_CONNECTOR_LVDS,
	DRM_MODE_CONNECTOR_eDP,
	DRM_MODE_CONNECTOR_DSI,
	};

	drmModeConnector* main_monitor_connector = nullptr;
	unsigned i = 0;
	do {
	main_monitor_connector = find_used_connector_by_type(fd, resources, kConnectorPriority[i]);
	i++;
	} while (!main_monitor_connector && i < ARRAY_SIZE(kConnectorPriority));

	/* If we didn't find a connector, grab the first one that is connected. */
	if (!main_monitor_connector) {
	main_monitor_connector = find_first_connected_connector(fd, resources);
	}

	/* If we still didn't find a connector, give up and return. */
	if (!main_monitor_connector) return nullptr;

	*mode_index = 0;
	for (int modes = 0; modes < main_monitor_connector->count_modes; modes++) {
	if (main_monitor_connector->modes[modes].type & DRM_MODE_TYPE_PREFERRED) {
	*mode_index = modes;
	break;
	}
	}

	return main_monitor_connector;
	}

	void MinuiBackendDrm::DisableNonMainCrtcs(int fd, drmModeRes* resources, drmModeCrtc* main_crtc) {
	for (int i = 0; i < resources->count_connectors; i++) {
	drmModeConnector* connector = drmModeGetConnector(fd, resources->connectors[i]);
	drmModeCrtc* crtc = find_crtc_for_connector(fd, resources, connector);
	if (crtc->crtc_id != main_crtc->crtc_id) {
	DrmDisableCrtc(fd, crtc);
	}
	drmModeFreeCrtc(crtc);
	}
	}

	GRSurface* MinuiBackendDrm::Init() {
	drmModeRes* res = nullptr;

	/* Consider DRM devices in order. */
	for (int i = 0; i < DRM_MAX_MINOR; i++) {
	char* dev_name;
	int ret = asprintf(&dev_name, DRM_DEV_NAME, DRM_DIR_NAME, i);
	if (ret < 0) continue;

	drm_fd = open(dev_name, O_RDWR, 0);
	free(dev_name);
	if (drm_fd < 0) continue;

	uint64_t cap = 0;
	/* We need dumb buffers. */
	ret = drmGetCap(drm_fd, DRM_CAP_DUMB_BUFFER, &cap);
	if (ret \|\| cap == 0) {
	close(drm_fd);
	continue;
	}

	res = drmModeGetResources(drm_fd);
	if (!res) {
	close(drm_fd);
	continue;
	}

	/* Use this device if it has at least one connected monitor. */
	if (res->count_crtcs > 0 && res->count_connectors > 0) {
	if (find_first_connected_connector(drm_fd, res)) break;
	}

	drmModeFreeResources(res);
	close(drm_fd);
	res = nullptr;
	}

	if (drm_fd < 0 \|\| res == nullptr) {
	perror("cannot find/open a drm device");
	return nullptr;
	}

	uint32_t selected_mode;
	main_monitor_connector = FindMainMonitor(drm_fd, res, &selected_mode);

	if (!main_monitor_connector) {
	printf("main_monitor_connector not found\n");
	drmModeFreeResources(res);
	close(drm_fd);
	return nullptr;
	}

	main_monitor_crtc = find_crtc_for_connector(drm_fd, res, main_monitor_connector);

	if (!main_monitor_crtc) {
	printf("main_monitor_crtc not found\n");
	drmModeFreeResources(res);
	close(drm_fd);
	return nullptr;
	}

	DisableNonMainCrtcs(drm_fd, res, main_monitor_crtc);

	main_monitor_crtc->mode = main_monitor_connector->modes[selected_mode];

	int width = main_monitor_crtc->mode.hdisplay;
	int height = main_monitor_crtc->mode.vdisplay;

	drmModeFreeResources(res);

	GRSurfaceDrms[0] = DrmCreateSurface(width, height);
	GRSurfaceDrms[1] = DrmCreateSurface(width, height);
	if (!GRSurfaceDrms[0] \|\| !GRSurfaceDrms[1]) {
	// GRSurfaceDrms and drm_fd should be freed in d'tor.
	return nullptr;
	}

	current_buffer = 0;

	// We will likely encounter errors in the backend functions (i.e. Flip) if EnableCrtc fails.
	if (DrmEnableCrtc(drm_fd, main_monitor_crtc, GRSurfaceDrms[1]) != 0) {
	return nullptr;
	}

	return GRSurfaceDrms[0];
	}

	static void page_flip_complete(__unused int fd,
	__unused unsigned int sequence,
	__unused unsigned int tv_sec,
	__unused unsigned int tv_usec,
	void *user_data) {
	static_cast<bool>(user_data) = false;
	}

	GRSurface* MinuiBackendDrm::Flip() {
	bool ongoing_flip = true;

	int ret = drmModePageFlip(drm_fd, main_monitor_crtc->crtc_id,
	GRSurfaceDrms[current_buffer]->fb_id,
	DRM_MODE_PAGE_FLIP_EVENT, &ongoing_flip);
	if (ret < 0) {
	printf("drmModePageFlip failed ret=%d\n", ret);
	return nullptr;
	}

	while (ongoing_flip) {
	struct pollfd fds = {
	.fd = drm_fd,
	.events = POLLIN
	};

	ret = poll(&fds, 1, -1);
	if (ret == -1 \|\| !(fds.revents & POLLIN)) {
	printf("poll() failed on drm fd\n");
	break;
	}

	drmEventContext evctx = {
	.version = DRM_EVENT_CONTEXT_VERSION,
	.page_flip_handler = page_flip_complete
	};

	ret = drmHandleEvent(drm_fd, &evctx);
	if (ret != 0) {
	printf("drmHandleEvent failed ret=%d\n", ret);
	break;
	}
	}

	current_buffer = 1 - current_buffer;
	return GRSurfaceDrms[current_buffer];
	}

	MinuiBackendDrm::~MinuiBackendDrm() {
	DrmDisableCrtc(drm_fd, main_monitor_crtc);
	DrmDestroySurface(GRSurfaceDrms[0]);
	DrmDestroySurface(GRSurfaceDrms[1]);
	drmModeFreeCrtc(main_monitor_crtc);
	drmModeFreeConnector(main_monitor_connector);
	close(drm_fd);
	drm_fd = -1;
	}