add drm_test to test drmWaitVBlank

demos/drm_test.cc

@@ -0,0 +1,77 @@
+/**
+ * used to test drm api
+ *  g++ -std=c++1y `pkg-config libdrm --libs --cflags ` drm_test.cc
+ */
+
+#include <xf86drm.h>
+#include <xf86drmMode.h>
+
+#include <cstdio>
+#include <cstdlib>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <fcntl.h>
+
+#include <iostream>
+#include <vector>
+#include <algorithm>
+
+using namespace std;
+
+static int dfd = -1;
+
+int main(int argc, char *argv[])
+{
+    if (!drmAvailable()) {
+        cerr << "drm not available" << endl;
+        return -1;
+    }
+
+    dfd = drmOpen("i915", NULL);
+    if (dfd < 0) {
+        cerr << "drmOpen failed, try raw open" << endl;
+        dfd = open("/dev/dri/card0", O_RDWR);
+        if (dfd <= 0) {
+            cerr << "drm open failed" << endl;
+            return -1;
+        }
+    }
+
+    float fps = 0.0;
+    vector<int> intervals;
+
+    drmVBlank vblk;
+
+    vblk.request.sequence = 1;
+    vblk.request.type = DRM_VBLANK_RELATIVE;
+
+    struct timeval tv = {0};
+    bool quit = false;
+    int limit  = 100;
+    while (!quit && limit-- > 0) {
+        int ret = drmWaitVBlank(dfd, &vblk);
+
+        int old = tv.tv_sec * 1000 + tv.tv_usec / 1000;
+        int sec = vblk.reply.tval_sec * 1000 + vblk.reply.tval_usec/1000;
+
+        cerr << "drmWaitVBlank reply: seq " << vblk.reply.sequence 
+            << ", interval: " <<  sec - old
+            << endl;
+
+        vblk.request.type = DRM_VBLANK_RELATIVE;
+        vblk.request.sequence = 1;
+
+        tv.tv_sec = vblk.reply.tval_sec;
+        tv.tv_usec = vblk.reply.tval_usec;
+
+        if (old) intervals.emplace_back(sec - old);
+    }
+
+    auto sum = std::accumulate(intervals.begin(), intervals.end(), 0);
+    fps = 1000.0f * intervals.size() / sum;
+    cerr << "estimated fps: " << fps << endl;
+
+    drmClose(dfd);
+
+    return 0;
+}