1 files changed, 38 insertions, 12 deletions

diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 3614b2ed..e0d22012 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -724,6 +724,26 @@ int V4L2VideoDevice::getFormat(V4L2DeviceFormat *format)
 }
 
 /**
+ * \brief Try an image format on the V4L2 video device
+ * \param[inout] format The image format to test applicability to the video device
+ *
+ * Try the supplied \a format on the video device without applying it, returning
+ * the format that would be applied. This is equivalent to setFormat(), except
+ * that the device configuration is not changed.
+ *
+ * \return 0 on success or a negative error code otherwise
+ */
+int V4L2VideoDevice::tryFormat(V4L2DeviceFormat *format)
+{
+	if (caps_.isMeta())
+		return trySetFormatMeta(format, false);
+	else if (caps_.isMultiplanar())
+		return trySetFormatMultiplane(format, false);
+	else
+		return trySetFormatSingleplane(format, false);
+}
+
+/**
  * \brief Configure an image format on the V4L2 video device
  * \param[inout] format The image format to apply to the video device
  *
@@ -735,11 +755,11 @@ int V4L2VideoDevice::getFormat(V4L2DeviceFormat *format)
 int V4L2VideoDevice::setFormat(V4L2DeviceFormat *format)
 {
 	if (caps_.isMeta())
-		return setFormatMeta(format);
+		return trySetFormatMeta(format, true);
 	else if (caps_.isMultiplanar())
-		return setFormatMultiplane(format);
+		return trySetFormatMultiplane(format, true);
 	else
-		return setFormatSingleplane(format);
+		return trySetFormatSingleplane(format, true);
 }
 
 int V4L2VideoDevice::getFormatMeta(V4L2DeviceFormat *format)
@@ -765,7 +785,7 @@ int V4L2VideoDevice::getFormatMeta(V4L2DeviceFormat *format)
 	return 0;
 }
 
-int V4L2VideoDevice::setFormatMeta(V4L2DeviceFormat *format)
+int V4L2VideoDevice::trySetFormatMeta(V4L2DeviceFormat *format, bool set)
 {
 	struct v4l2_format v4l2Format = {};
 	struct v4l2_meta_format *pix = &v4l2Format.fmt.meta;
@@ -774,9 +794,11 @@ int V4L2VideoDevice::setFormatMeta(V4L2DeviceFormat *format)
 	v4l2Format.type = bufferType_;
 	pix->dataformat = format->fourcc;
 	pix->buffersize = format->planes[0].size;
-	ret = ioctl(VIDIOC_S_FMT, &v4l2Format);
+	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
 	if (ret) {
-		LOG(V4L2, Error) << "Unable to set format: " << strerror(-ret);
+		LOG(V4L2, Error)
+			<< "Unable to " << (set ? "set" : "try")
+			<< " format: " << strerror(-ret);
 		return ret;
 	}
 
@@ -820,7 +842,7 @@ int V4L2VideoDevice::getFormatMultiplane(V4L2DeviceFormat *format)
 	return 0;
 }
 
-int V4L2VideoDevice::setFormatMultiplane(V4L2DeviceFormat *format)
+int V4L2VideoDevice::trySetFormatMultiplane(V4L2DeviceFormat *format, bool set)
 {
 	struct v4l2_format v4l2Format = {};
 	struct v4l2_pix_format_mplane *pix = &v4l2Format.fmt.pix_mp;
@@ -838,9 +860,11 @@ int V4L2VideoDevice::setFormatMultiplane(V4L2DeviceFormat *format)
 		pix->plane_fmt[i].sizeimage = format->planes[i].size;
 	}
 
-	ret = ioctl(VIDIOC_S_FMT, &v4l2Format);
+	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
 	if (ret) {
-		LOG(V4L2, Error) << "Unable to set format: " << strerror(-ret);
+		LOG(V4L2, Error)
+			<< "Unable to " << (set ? "set" : "try")
+			<< " format: " << strerror(-ret);
 		return ret;
 	}
 
@@ -883,7 +907,7 @@ int V4L2VideoDevice::getFormatSingleplane(V4L2DeviceFormat *format)
 	return 0;
 }
 
-int V4L2VideoDevice::setFormatSingleplane(V4L2DeviceFormat *format)
+int V4L2VideoDevice::trySetFormatSingleplane(V4L2DeviceFormat *format, bool set)
 {
 	struct v4l2_format v4l2Format = {};
 	struct v4l2_pix_format *pix = &v4l2Format.fmt.pix;
@@ -895,9 +919,11 @@ int V4L2VideoDevice::setFormatSingleplane(V4L2DeviceFormat *format)
 	pix->pixelformat = format->fourcc;
 	pix->bytesperline = format->planes[0].bpl;
 	pix->field = V4L2_FIELD_NONE;
-	ret = ioctl(VIDIOC_S_FMT, &v4l2Format);
+	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
 	if (ret) {
-		LOG(V4L2, Error) << "Unable to set format: " << strerror(-ret);
+		LOG(V4L2, Error)
+			<< "Unable to " << (set ? "set" : "try")
+			<< " format: " << strerror(-ret);
 		return ret;
 	}