Fix sff panic deadlock, share the evdev probe, assorted review cleanups

harness/stream.go

@@ -12,8 +12,10 @@ import (
 	"net/http"
 	"os"
 	"sync"
+	"time"
 
 	"g.fc.run/theater/cabletest/internal/drm"
+	"g.fc.run/theater/cabletest/internal/evdev"
 )
 
 const streamAddr = ":8080"
@@ -115,7 +117,7 @@ func serveStream() error {
 	if err != nil {
 		return err
 	}
-	if touchscreen, err = openTouchscreen(); err != nil {
+	if touchscreen, err = evdev.FindTouchscreen(os.O_RDWR); err != nil {
 		return err
 	}
 	ln, err := net.Listen("tcp", streamAddr)
@@ -158,7 +160,10 @@ func keys(w http.ResponseWriter, r *http.Request) {
 
 // Between runs the crtc scans out the console framebuffer, which is not a
 // dumb buffer and fails to map on every frame; each error reads once, not at
-// frame rate.
+// frame rate. The pause paces the retry, since a failure ahead of the vblank
+// wait would otherwise spin hot.
+const captureErrPause = 100 * time.Millisecond
+
 func captureLoop(g *grabber) {
 	lastErr := ""
 	for {
@@ -168,6 +173,7 @@ func captureLoop(g *grabber) {
 				lastErr = err.Error()
 				fmt.Fprintf(os.Stderr, "capture: %v\n", err)
 			}
+			time.Sleep(captureErrPause)
 			continue
 		}
 		lastErr = ""