media/gpu/v4l2: add V4L2Queue::TryFormat()

We were using SetFormat() when we wanted to just test the availability
of a given format on a device. This is a bit misleading for the reader.

Implement and use TryFormat(), which properly uses the TRY_FORMAT ioctl,
and use it where relevant.

BUG=None
TEST=video.DecodeAccel.h264 passed on Trogdor

Change-Id: I223a2911451bae753e8560180ccdaa5a3502a1db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2422103
Commit-Queue: Fritz Koenig <frkoenig@chromium.org>
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Auto-Submit: Alexandre Courbot <acourbot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809404}

media/gpu/v4l2/v4l2_device.cc

@@ -52,6 +52,22 @@ gfx::Rect V4L2RectToGfxRect(const v4l2_rect& rect) {
   return gfx::Rect(rect.left, rect.top, rect.width, rect.height);
 }
 
+struct v4l2_format BuildV4L2Format(const enum v4l2_buf_type type,
+                                   uint32_t fourcc,
+                                   const gfx::Size& size,
+                                   size_t buffer_size) {
+  struct v4l2_format format;
+  memset(&format, 0, sizeof(format));
+  format.type = type;
+  format.fmt.pix_mp.pixelformat = fourcc;
+  format.fmt.pix_mp.width = size.width();
+  format.fmt.pix_mp.height = size.height();
+  format.fmt.pix_mp.num_planes = V4L2Device::GetNumPlanesOfV4L2PixFmt(fourcc);
+  format.fmt.pix_mp.plane_fmt[0].sizeimage = buffer_size;
+
+  return format;
+}
+
 }  // namespace
 
 V4L2ExtCtrl::V4L2ExtCtrl(uint32_t id) {
@@ -922,13 +938,7 @@ V4L2Queue::~V4L2Queue() {
 base::Optional<struct v4l2_format> V4L2Queue::SetFormat(uint32_t fourcc,
                                                         const gfx::Size& size,
                                                         size_t buffer_size) {
-  struct v4l2_format format = {};
-  format.type = type_;
-  format.fmt.pix_mp.pixelformat = fourcc;
-  format.fmt.pix_mp.width = size.width();
-  format.fmt.pix_mp.height = size.height();
-  format.fmt.pix_mp.num_planes = V4L2Device::GetNumPlanesOfV4L2PixFmt(fourcc);
-  format.fmt.pix_mp.plane_fmt[0].sizeimage = buffer_size;
+  struct v4l2_format format = BuildV4L2Format(type_, fourcc, size, buffer_size);
   if (device_->Ioctl(VIDIOC_S_FMT, &format) != 0 ||
       format.fmt.pix_mp.pixelformat != fourcc) {
     VPQLOGF(2) << "Failed to set format (format_fourcc=0x" << std::hex << fourcc
@@ -940,6 +950,20 @@ base::Optional<struct v4l2_format> V4L2Queue::SetFormat(uint32_t fourcc,
   return current_format_;
 }
 
+base::Optional<struct v4l2_format> V4L2Queue::TryFormat(uint32_t fourcc,
+                                                        const gfx::Size& size,
+                                                        size_t buffer_size) {
+  struct v4l2_format format = BuildV4L2Format(type_, fourcc, size, buffer_size);
+  if (device_->Ioctl(VIDIOC_TRY_FMT, &format) != 0 ||
+      format.fmt.pix_mp.pixelformat != fourcc) {
+    VPQLOGF(2) << "Tried format not supported (format_fourcc=0x" << std::hex
+               << fourcc << ")";
+    return base::nullopt;
+  }
+
+  return format;
+}
+
 std::pair<base::Optional<struct v4l2_format>, int> V4L2Queue::GetFormat() {
   struct v4l2_format format;
   memset(&format, 0, sizeof(format));

media/gpu/v4l2/v4l2_device.h

@@ -308,6 +308,15 @@ class MEDIA_GPU_EXPORT V4L2Queue
                                                size_t buffer_size)
       WARN_UNUSED_RESULT;
 
+  // Identical to |SetFormat|, but does not actually apply the format, and can
+  // be called anytime.
+  // Returns an adjusted V4L2 format if |fourcc| is supported by the queue, or
+  // |nullopt| if |fourcc| is not supported or an ioctl error happened.
+  base::Optional<struct v4l2_format> TryFormat(uint32_t fourcc,
+                                               const gfx::Size& size,
+                                               size_t buffer_size)
+      WARN_UNUSED_RESULT;
+
   // Returns the currently set format on the queue. The result is returned as
   // a std::pair where the first member is the format, or base::nullopt if the
   // format could not be obtained due to an ioctl error. The second member is

media/gpu/v4l2/v4l2_video_decoder.cc

@@ -292,7 +292,7 @@ bool V4L2VideoDecoder::SetupOutputFormat(const gfx::Size& size,
     }
 
     base::Optional<struct v4l2_format> format =
-        output_queue_->SetFormat(pixfmt, size, 0);
+        output_queue_->TryFormat(pixfmt, size, 0);
     if (!format)
       continue;