Support Linux DRM backend

Implemented DRM-based framebuffer setup, including:
 - Opening DRM device
 - Creating dumb buffers and mapping them to framebuffers
 - Setting mode and handling CRTC for connected display output

Currently, using the DRM legacy interface is suitable for Mado's backend
if we only need basic window display without advanced features. The DRM
legacy is simpler to implement.

Close #60

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

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"