Support Linux DRM backend

Makefile

@@ -117,6 +117,15 @@ libtwin.a_files-y += backend/fbdev.c
 libtwin.a_files-y += backend/linux_input.c
 endif
 
+ifeq ($(CONFIG_BACKEND_DRM), y)
+BACKEND = drm
+TARGET_LIBS += -ludev
+libtwin.a_files-y += backend/drm.c
+libtwin.a_files-y += backend/linux_input.c
+libtwin.a_cflags-y += $(shell pkg-config --cflags libdrm)
+TARGET_LIBS += $(shell pkg-config --libs libdrm)
+endif
+
 ifeq ($(CONFIG_BACKEND_VNC), y)
 BACKEND = vnc
 libtwin.a_files-y += backend/vnc.c

README.md

@@ -83,6 +83,9 @@ For SDL backend, install the [SDL2 library](https://www.libsdl.org/).
 * macOS: `brew install sdl2`
 * Ubuntu Linux / Debian: `sudo apt install libsdl2-dev`
 
+For DRM backend, install the [libdrm](https://gitlab.freedesktop.org/mesa/drm).
+* Ubuntu Linux / Debian: `sudo apt install libdrm-dev`
+
 For the VNC backend, please note that it has only been tested on GNU/Linux, and the prebuilt [neatvnc](https://github.com/any1/neatvnc) package might be outdated. To ensure you have the latest version, you can build the required packages from source by running the script:
 ```shell
 $ tools/build-neatvnc.sh
@@ -128,6 +131,14 @@ $ sudo usermod -a -G video $USERNAME
 
 In addition, the framebuffer device can be assigned via the environment variable `FRAMEBUFFER`.
 
+To run demo program with the DRM backend:
+
+```shell
+$ sudo ./demo-drm
+```
+
+The DRM device can be assigened via the environment variable `DRI_CARD`.
+
 To run demo program with the VNC backend:
 
 ```shell

backend/drm.c

@@ -0,0 +1,300 @@
+/*
+ * Twin - A Tiny Window System
+ * Copyright (c) 2024 National Cheng Kung University, Taiwan
+ * All rights reserved.
+ */
+
+#include <fcntl.h>
+#include <libdrm/drm.h>
+#include <libdrm/drm_mode.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <twin.h>
+#include <unistd.h>
+#include <xf86drm.h>
+#include <xf86drmMode.h>
+
+#include "linux_input.h"
+#include "linux_vt.h"
+#include "twin_backend.h"
+
+#define DRM_DRI_NAME "DRI_CARD"
+#define DRM_DRI_DEFAULT "/dev/dri/card0"
+#define SCREEN(x) ((twin_context_t *) x)->screen
+#define RES(x) ((twin_drm_t *) x)->res
+#define CONN(x) ((twin_drm_t *) x)->conn
+#define CRTC(x) ((twin_drm_t *) x)->crtc
+#define PRIV(x) ((twin_drm_t *) ((twin_context_t *) x)->priv)
+
+typedef struct {
+    twin_screen_t *screen;
+
+    /* Linux input system */
+    void *input;
+
+    /* Linux virtual terminal (VT) */
+    int vt_fd;
+
+    /* DRM driver */
+    int width, height;
+    int drm_dri_fd;
+    drmModeResPtr res;
+    drmModeConnectorPtr conn;
+    drmModeCrtcPtr crtc;
+    uint32_t fb_id;
+    uint8_t *fb_base;
+    size_t fb_len;
+} twin_drm_t;
+
+static void _twin_drm_put_span(twin_coord_t left,
+                               twin_coord_t top,
+                               twin_coord_t right,
+                               twin_argb32_t *pixels,
+                               void *closure)
+{
+    twin_drm_t *tx = PRIV(closure);
+
+    if (tx->fb_base == MAP_FAILED)
+        return;
+
+    twin_coord_t width = right - left;
+    off_t off = tx->width * top + left;
+    uint32_t *dest =
+        (uint32_t *) ((uintptr_t) tx->fb_base + (off * sizeof(*dest)));
+    memcpy(dest, pixels, width * sizeof(*dest));
+}
+
+static void twin_drm_get_screen_size(twin_drm_t *tx, int *width, int *height)
+{
+    *width = CONN(tx)->modes[0].hdisplay;
+    *height = CONN(tx)->modes[0].vdisplay;
+}
+
+static bool twin_drm_work(void *closure)
+{
+    twin_screen_t *screen = SCREEN(closure);
+
+    if (twin_screen_damaged(screen))
+        twin_screen_update(screen);
+
+    return true;
+}
+
+static bool get_resources(int fd, drmModeResPtr *resources)
+{
+    *resources = drmModeGetResources(fd);
+    if (*resources == NULL) {
+        log_error("Failed to get resources");
+        return false;
+    }
+    return true;
+}
+
+static drmModeConnectorPtr find_drm_connector(int fd, drmModeResPtr resources)
+{
+    drmModeConnectorPtr connector_ptr = NULL;
+
+    for (int i = 0; i < resources->count_connectors; i++) {
+        connector_ptr = drmModeGetConnector(fd, resources->connectors[i]);
+        if (connector_ptr && connector_ptr->connection == DRM_MODE_CONNECTED) {
+            /* it's connected, let's use this! */
+            break;
+        }
+        drmModeFreeConnector(connector_ptr);
+        connector_ptr = NULL;
+    }
+
+    return connector_ptr;
+}
+
+static bool create_fb(twin_drm_t *tx)
+{
+    /* Create dumb buffer */
+    struct drm_mode_create_dumb create_req = {
+        .width = tx->width,
+        .height = tx->height,
+        .bpp = 32,
+    };
+    if (ioctl(tx->drm_dri_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_req) < 0) {
+        log_error("Cannot create dumb buffer");
+        return false;
+    }
+    tx->fb_len = create_req.size;
+
+    /* Create framebuffer object for the dumb-buffer */
+    if (drmModeAddFB(tx->drm_dri_fd, tx->width, tx->height, 24, 32,
+                     create_req.pitch, create_req.handle, &tx->fb_id) != 0) {
+        log_error("Cannot create framebubber");
+        return false;
+    }
+
+    /* Prepare buffer for memory mapping */
+    struct drm_mode_map_dumb map_req = {
+        .handle = create_req.handle,
+    };
+    if (ioctl(tx->drm_dri_fd, DRM_IOCTL_MODE_MAP_DUMB, &map_req) < 0) {
+        log_error("Cannot map dumb buffer");
+        goto bail_fb;
+    }
+
+    /* Perform actual memory mapping */
+    tx->fb_base = mmap(NULL, tx->fb_len, PROT_READ | PROT_WRITE, MAP_SHARED,
+                       tx->drm_dri_fd, map_req.offset);
+    if (tx->fb_base == MAP_FAILED) {
+        log_error("Failed to mmap framebuffer");
+        goto bail_fb;
+    }
+
+    return true;
+
+bail_fb:
+    drmModeRmFB(tx->drm_dri_fd, tx->fb_id);
+    return false;
+}
+
+static bool twin_drm_apply_config(twin_drm_t *tx)
+{
+    /* Retrieve resources */
+    if (!get_resources(tx->drm_dri_fd, &RES(tx)))
+        return false;
+
+    /* Find a connected connector */
+    CONN(tx) = find_drm_connector(tx->drm_dri_fd, RES(tx));
+    if (!CONN(tx))
+        goto bail_res;
+
+    /* Get the mode information */
+    drmModeModeInfo mode = CONN(tx)->modes[0];
+    tx->width = mode.hdisplay;
+    tx->height = mode.vdisplay;
+
+    /* Create the framebuffer */
+    if (!create_fb(tx))
+        goto bail_conn;
+
+    /* Set the mode on a CRTC */
+    CRTC(tx) = drmModeGetCrtc(tx->drm_dri_fd, RES(tx)->crtcs[0]);
+    if (!CRTC(tx))
+        goto bail_mmap;
+
+    if (drmModeSetCrtc(tx->drm_dri_fd, CRTC(tx)->crtc_id, tx->fb_id, 0, 0,
+                       &CONN(tx)->connector_id, 1, &mode) != 0) {
+        log_error("Failed to set CRTC");
+        goto bail_crtc;
+    }
+
+    return true;
+
+bail_crtc:
+    drmModeFreeCrtc(CRTC(tx));
+bail_mmap:
+    munmap(tx->fb_base, tx->fb_len);
+    drmModeRmFB(tx->drm_dri_fd, tx->fb_id);
+bail_conn:
+    drmModeFreeConnector(CONN(tx));
+bail_res:
+    drmModeFreeResources(RES(tx));
+    return false;
+}
+
+twin_context_t *twin_drm_init(int width, int height)
+{
+    /* Get environment variable to execute */
+    char *drm_dri_path = getenv(DRM_DRI_NAME);
+    if (!drm_dri_path) {
+        log_info("Environment variable $DRI_CARD not set, use %s by default",
+                 DRM_DRI_DEFAULT);
+        drm_dri_path = DRM_DRI_DEFAULT;
+    }
+
+    twin_context_t *ctx = calloc(1, sizeof(twin_context_t));
+    if (!ctx)
+        return NULL;
+
+    ctx->priv = calloc(1, sizeof(twin_drm_t));
+    if (!ctx->priv)
+        return NULL;
+
+    twin_drm_t *tx = ctx->priv;
+
+    /* Open the DRM driver */
+    tx->drm_dri_fd = open(drm_dri_path, O_RDWR);
+    if (tx->drm_dri_fd < 0) {
+        log_error("Failed to open %s", drm_dri_path);
+        goto bail;
+    }
+
+    /* Set up virtual terminal environment */
+    if (!twin_vt_setup(&tx->vt_fd)) {
+        goto bail_dri_card_fd;
+    }
+
+    /* Apply configurations to the DRM driver*/
+    if (!twin_drm_apply_config(tx)) {
+        log_error("Failed to apply configurations to the DRM driver");
+        goto bail_vt_fd;
+    }
+
+    /* Create TWIN screen */
+    ctx->screen =
+        twin_screen_create(width, height, NULL, _twin_drm_put_span, ctx);
+
+    /* Create Linux input system object */
+    tx->input = twin_linux_input_create(ctx->screen);
+    if (!tx->input) {
+        log_error("Failed to create Linux input system object");
+        goto bail_screen;
+    }
+
+    /* Setup file handler and work functions */
+    twin_set_work(twin_drm_work, TWIN_WORK_REDISPLAY, ctx);
+
+    return ctx;
+
+bail_screen:
+    twin_screen_destroy(ctx->screen);
+bail_vt_fd:
+    close(tx->vt_fd);
+bail_dri_card_fd:
+    close(tx->drm_dri_fd);
+bail:
+    free(ctx->priv);
+    free(ctx);
+    return NULL;
+}
+
+static void twin_drm_configure(twin_context_t *ctx)
+{
+    int width, height;
+    twin_drm_t *tx = PRIV(ctx);
+    twin_drm_get_screen_size(tx, &width, &height);
+    twin_screen_resize(SCREEN(ctx), width, height);
+}
+
+static void twin_drm_exit(twin_context_t *ctx)
+{
+    if (!ctx)
+        return;
+
+    twin_drm_t *tx = PRIV(ctx);
+    twin_vt_mode(tx->vt_fd, KD_TEXT);
+    drmModeFreeCrtc(CRTC(tx));
+    munmap(tx->fb_base, tx->fb_len);
+    drmModeRmFB(tx->drm_dri_fd, tx->fb_id);
+    drmModeFreeConnector(CONN(tx));
+    drmModeFreeResources(RES(tx));
+    twin_linux_input_destroy(tx->input);
+    close(tx->vt_fd);
+    close(tx->drm_dri_fd);
+    free(ctx->priv);
+    free(ctx);
+}
+
+/* Register the Linux DRM backend */
+
+const twin_backend_t g_twin_backend = {
+    .init = twin_drm_init,
+    .configure = twin_drm_configure,
+    .exit = twin_drm_exit,
+};

configs/Kconfig

@@ -12,6 +12,10 @@ config BACKEND_FBDEV
     bool "Linux framebuffer support"
     select CURSOR
 
+config BACKEND_DRM
+    bool "Linux DRM support"
+    select CURSOR
+
 config BACKEND_SDL
     bool "SDL video output support"