libv4l: use driver read() when possible

From: Hans de Goede <j.w.r.degoede@hhs.nl>

When the driver supports read() and we are not converting let the driver
handle read() instead of emulating it with mmap mode

Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>

1 files changed, 12 insertions, 0 deletions

diff --git a/v4l2-apps/lib/libv4l/libv4l2/libv4l2.c b/v4l2-apps/lib/libv4l/libv4l2/libv4l2.c
index fc41c665d..a40ab4ffe 100644
--- a/v4l2-apps/lib/libv4l/libv4l2/libv4l2.c
+++ b/v4l2-apps/lib/libv4l/libv4l2/libv4l2.c
@@ -75,6 +75,7 @@
 #define V4L2_STREAMON			0x0100
 #define V4L2_BUFFERS_REQUESTED_BY_READ	0x0200
 #define V4L2_STREAM_CONTROLLED_BY_READ	0x0400
+#define V4L2_SUPPORTS_READ		0x0800
 
 #define V4L2_MMAP_OFFSET_MAGIC      0xABCDEF00u
 
@@ -456,6 +457,8 @@ int v4l2_fd_open(int fd, int v4l2_flags)
   }
 
   devices[index].flags = v4l2_flags;
+  if (cap.capabilities & V4L2_CAP_READWRITE)
+    devices[index].flags |= V4L2_SUPPORTS_READ;
   devices[index].open_count = 1;
   devices[index].src_fmt = fmt;
   devices[index].dest_fmt = fmt;
@@ -908,6 +911,15 @@ ssize_t v4l2_read (int fd, void* buffer, size_t n)
 
   pthread_mutex_lock(&devices[index].stream_lock);
 
+  /* When not converting and the device supports read let the kernel handle
+     it */
+  if ((devices[index].flags & V4L2_SUPPORTS_READ) &&
+      devices[index].src_fmt.fmt.pix.pixelformat ==
+      devices[index].dest_fmt.fmt.pix.pixelformat) {
+    result = syscall(SYS_read, fd, buffer, n);
+    goto leave;
+  }
+
   if (!(devices[index].flags & V4L2_STREAM_CONTROLLED_BY_READ)) {
     if ((devices[index].flags & V4L2_STREAMON) ||
 	devices[index].frame_queued) {