minui/graphics_drm.cpp - platform/bootable/recovery - Git at Google

 /*
  * 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 <memory>

 #include <android-base/macros.h>
 #include <android-base/stringprintf.h>
 #include <android-base/unique_fd.h>
 #include <drm_fourcc.h>
 #include <xf86drm.h>
 #include <xf86drmMode.h>

 #include "minui/minui.h"

 GRSurfaceDrm::~GRSurfaceDrm() {
   if (mmapped_buffer_) {
     munmap(mmapped_buffer_, row_bytes * height);
   }

   if (fb_id) {
     if (drmModeRmFB(drm_fd_, fb_id) != 0) {
       perror("Failed to drmModeRmFB");
       // Falling through to free other resources.
     }
   }

   if (handle) {
     drm_gem_close gem_close = {};
     gem_close.handle = handle;

     if (drmIoctl(drm_fd_, DRM_IOCTL_GEM_CLOSE, &gem_close) != 0) {
       perror("Failed to DRM_IOCTL_GEM_CLOSE");
     }
   }
 }

 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;
   }
 }

 std::unique_ptr<GRSurfaceDrm> GRSurfaceDrm::Create(int drm_fd, int width, int height) {
   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;

   if (drmIoctl(drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb) != 0) {
     perror("Failed to DRM_IOCTL_MODE_CREATE_DUMB");
     return nullptr;
   }

   // Cannot use std::make_unique to access non-public ctor.
   auto surface = std::unique_ptr<GRSurfaceDrm>(new GRSurfaceDrm(
       width, height, create_dumb.pitch, create_dumb.bpp / 8, drm_fd, create_dumb.handle));

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

   handles[0] = surface->handle;
   pitches[0] = create_dumb.pitch;
   offsets[0] = 0;
   if (drmModeAddFB2(drm_fd, width, height, format, handles, pitches, offsets, &surface->fb_id, 0) !=
       0) {
     perror("Failed to drmModeAddFB2");
     return nullptr;
   }

   drm_mode_map_dumb map_dumb = {};
   map_dumb.handle = create_dumb.handle;
   if (drmIoctl(drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb) != 0) {
     perror("Failed to DRM_IOCTL_MODE_MAP_DUMB");
     return nullptr;
   }

   auto mmapped = mmap(nullptr, surface->height * surface->row_bytes, PROT_READ | PROT_WRITE,
                       MAP_SHARED, drm_fd, map_dumb.offset);
   if (mmapped == MAP_FAILED) {
     perror("Failed to mmap()");
     return nullptr;
   }
   surface->mmapped_buffer_ = static_cast<uint8_t*>(mmapped);
   return surface;
 }

 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
   }
 }

 bool MinuiBackendDrm::DrmEnableCrtc(int drm_fd, drmModeCrtc* crtc,
                                     const std::unique_ptr<GRSurfaceDrm>& surface) {
   if (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) != 0) {
     perror("Failed to drmModeSetCrtc");
     return false;
   }
   return true;
 }

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

 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 < arraysize(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;
   drm_fd = -1;

   /* Consider DRM devices in order. */
   for (int i = 0; i < DRM_MAX_MINOR; i++) {
     auto dev_name = android::base::StringPrintf(DRM_DEV_NAME, DRM_DIR_NAME, i);
     android::base::unique_fd fd(open(dev_name.c_str(), O_RDWR | O_CLOEXEC));
     if (fd == -1) continue;

     /* We need dumb buffers. */
     if (uint64_t cap = 0; drmGetCap(fd.get(), DRM_CAP_DUMB_BUFFER, &cap) != 0 || cap == 0) {
       continue;
     }

     res = drmModeGetResources(fd.get());
     if (!res) {
       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(fd.get(), res)) {
         drm_fd = fd.release();
         break;
       }
     }

     drmModeFreeResources(res);
     res = nullptr;
   }

   if (drm_fd == -1 || res == nullptr) {
     perror("Failed to find/open a drm device");
     return nullptr;
   }

   uint32_t selected_mode;
   main_monitor_connector = FindMainMonitor(drm_fd, res, &selected_mode);
   if (!main_monitor_connector) {
     fprintf(stderr, "Failed to find main_monitor_connector\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) {
     fprintf(stderr, "Failed to find main_monitor_crtc\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] = GRSurfaceDrm::Create(drm_fd, width, height);
   GRSurfaceDrms[1] = GRSurfaceDrm::Create(drm_fd, width, height);
   if (!GRSurfaceDrms[0] || !GRSurfaceDrms[1]) {
     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])) {
     return nullptr;
   }

   return GRSurfaceDrms[0].get();
 }

 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;
   if (drmModePageFlip(drm_fd, main_monitor_crtc->crtc_id, GRSurfaceDrms[current_buffer]->fb_id,
                       DRM_MODE_PAGE_FLIP_EVENT, &ongoing_flip) != 0) {
     perror("Failed to drmModePageFlip");
     return nullptr;
   }

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

     if (poll(&fds, 1, -1) == -1 || !(fds.revents & POLLIN)) {
       perror("Failed to poll() on drm fd");
       break;
     }

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

     if (drmHandleEvent(drm_fd, &evctx) != 0) {
       perror("Failed to drmHandleEvent");
       break;
     }
   }

   current_buffer = 1 - current_buffer;
   return GRSurfaceDrms[current_buffer].get();
 }

 MinuiBackendDrm::~MinuiBackendDrm() {
   DrmDisableCrtc(drm_fd, main_monitor_crtc);
   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 <memory>

	#include <android-base/macros.h>
	#include <android-base/stringprintf.h>
	#include <android-base/unique_fd.h>
	#include <drm_fourcc.h>
	#include <xf86drm.h>
	#include <xf86drmMode.h>

	#include "minui/minui.h"

	GRSurfaceDrm::~GRSurfaceDrm() {
	if (mmapped_buffer_) {
	munmap(mmapped_buffer_, row_bytes * height);
	}

	if (fb_id) {
	if (drmModeRmFB(drm_fd_, fb_id) != 0) {
	perror("Failed to drmModeRmFB");
	// Falling through to free other resources.
	}
	}

	if (handle) {
	drm_gem_close gem_close = {};
	gem_close.handle = handle;

	if (drmIoctl(drm_fd_, DRM_IOCTL_GEM_CLOSE, &gem_close) != 0) {
	perror("Failed to DRM_IOCTL_GEM_CLOSE");
	}
	}
	}

	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;
	}
	}

	std::unique_ptr<GRSurfaceDrm> GRSurfaceDrm::Create(int drm_fd, int width, int height) {
	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;

	if (drmIoctl(drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb) != 0) {
	perror("Failed to DRM_IOCTL_MODE_CREATE_DUMB");
	return nullptr;
	}

	// Cannot use std::make_unique to access non-public ctor.
	auto surface = std::unique_ptr<GRSurfaceDrm>(new GRSurfaceDrm(
	width, height, create_dumb.pitch, create_dumb.bpp / 8, drm_fd, create_dumb.handle));

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

	handles[0] = surface->handle;
	pitches[0] = create_dumb.pitch;
	offsets[0] = 0;
	if (drmModeAddFB2(drm_fd, width, height, format, handles, pitches, offsets, &surface->fb_id, 0) !=
	0) {
	perror("Failed to drmModeAddFB2");
	return nullptr;
	}

	drm_mode_map_dumb map_dumb = {};
	map_dumb.handle = create_dumb.handle;
	if (drmIoctl(drm_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_dumb) != 0) {
	perror("Failed to DRM_IOCTL_MODE_MAP_DUMB");
	return nullptr;
	}

	auto mmapped = mmap(nullptr, surface->height * surface->row_bytes, PROT_READ \| PROT_WRITE,
	MAP_SHARED, drm_fd, map_dumb.offset);
	if (mmapped == MAP_FAILED) {
	perror("Failed to mmap()");
	return nullptr;
	}
	surface->mmapped_buffer_ = static_cast<uint8_t*>(mmapped);
	return surface;
	}

	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
	}
	}

	bool MinuiBackendDrm::DrmEnableCrtc(int drm_fd, drmModeCrtc* crtc,
	const std::unique_ptr<GRSurfaceDrm>& surface) {
	if (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) != 0) {
	perror("Failed to drmModeSetCrtc");
	return false;
	}
	return true;
	}

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

	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 < arraysize(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;
	drm_fd = -1;

	/* Consider DRM devices in order. */
	for (int i = 0; i < DRM_MAX_MINOR; i++) {
	auto dev_name = android::base::StringPrintf(DRM_DEV_NAME, DRM_DIR_NAME, i);
	android::base::unique_fd fd(open(dev_name.c_str(), O_RDWR \| O_CLOEXEC));
	if (fd == -1) continue;

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

	res = drmModeGetResources(fd.get());
	if (!res) {
	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(fd.get(), res)) {
	drm_fd = fd.release();
	break;
	}
	}

	drmModeFreeResources(res);
	res = nullptr;
	}

	if (drm_fd == -1 \|\| res == nullptr) {
	perror("Failed to find/open a drm device");
	return nullptr;
	}

	uint32_t selected_mode;
	main_monitor_connector = FindMainMonitor(drm_fd, res, &selected_mode);
	if (!main_monitor_connector) {
	fprintf(stderr, "Failed to find main_monitor_connector\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) {
	fprintf(stderr, "Failed to find main_monitor_crtc\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] = GRSurfaceDrm::Create(drm_fd, width, height);
	GRSurfaceDrms[1] = GRSurfaceDrm::Create(drm_fd, width, height);
	if (!GRSurfaceDrms[0] \|\| !GRSurfaceDrms[1]) {
	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])) {
	return nullptr;
	}

	return GRSurfaceDrms[0].get();
	}

	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;
	if (drmModePageFlip(drm_fd, main_monitor_crtc->crtc_id, GRSurfaceDrms[current_buffer]->fb_id,
	DRM_MODE_PAGE_FLIP_EVENT, &ongoing_flip) != 0) {
	perror("Failed to drmModePageFlip");
	return nullptr;
	}

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

	if (poll(&fds, 1, -1) == -1 \|\| !(fds.revents & POLLIN)) {
	perror("Failed to poll() on drm fd");
	break;
	}

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

	if (drmHandleEvent(drm_fd, &evctx) != 0) {
	perror("Failed to drmHandleEvent");
	break;
	}
	}

	current_buffer = 1 - current_buffer;
	return GRSurfaceDrms[current_buffer].get();
	}

	MinuiBackendDrm::~MinuiBackendDrm() {
	DrmDisableCrtc(drm_fd, main_monitor_crtc);
	drmModeFreeCrtc(main_monitor_crtc);
	drmModeFreeConnector(main_monitor_connector);
	close(drm_fd);
	drm_fd = -1;
	}