media: camss: Make use of V4L2_CAP_IO_MC

Implement mbus_code filtering for format enumeration.

Without this patch libcamera errors out with:
"ERROR V4L2 v4l2_videodevice.cpp:982 /dev/video0[cap]: Media bus code
filtering not supported by the device"

This is the second version of this change which handles the case of
several pixel formats corresponding to one media bus format correctly.
Signed-off-by: Andrey Konovalov <andrey.konovalov@linaro.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/qcom/camss/camss-video.c

@@ -539,6 +539,7 @@ static int video_enum_fmt(struct file *file, void *fh, struct v4l2_fmtdesc *f)
 {
 	struct camss_video *video = video_drvdata(file);
 	int i, j, k;
+	u32 mcode = f->mbus_code;
 
 	if (f->type != video->type)
 		return -EINVAL;
@@ -546,10 +547,26 @@ static int video_enum_fmt(struct file *file, void *fh, struct v4l2_fmtdesc *f)
 	if (f->index >= video->nformats)
 		return -EINVAL;
 
-	/* find index "i" of "k"th unique pixelformat in formats array */
+	/*
+	 * Find index "i" of "k"th unique pixelformat in formats array.
+	 *
+	 * If f->mbus_code passed to video_enum_fmt() is not zero, a device
+	 * with V4L2_CAP_IO_MC capability restricts enumeration to only the
+	 * pixel formats that can be produced from that media bus code.
+	 * This is implemented by skipping video->formats[] entries with
+	 * code != f->mbus_code (if f->mbus_code is not zero).
+	 * If the f->mbus_code passed to video_enum_fmt() is not supported,
+	 * -EINVAL is returned.
+	 * If f->mbus_code is zero, all the pixel formats are enumerated.
+	 */
 	k = -1;
 	for (i = 0; i < video->nformats; i++) {
+		if (mcode != 0 && video->formats[i].code != mcode)
+			continue;
+
 		for (j = 0; j < i; j++) {
+			if (mcode != 0 && video->formats[j].code != mcode)
+				continue;
 			if (video->formats[i].pixelformat ==
 					video->formats[j].pixelformat)
 				break;
@@ -563,6 +580,11 @@ static int video_enum_fmt(struct file *file, void *fh, struct v4l2_fmtdesc *f)
 	}
 
 	if (k < f->index)
+		/*
+		 * All the unique pixel formats matching the arguments
+		 * have been enumerated (k >= 0 and f->index > 0), or
+		 * no pixel formats match the non-zero f->mbus_code (k == -1).
+		 */
 		return -EINVAL;
 
 	f->pixelformat = video->formats[i].pixelformat;
@@ -949,8 +971,8 @@ int msm_video_register(struct camss_video *video, struct v4l2_device *v4l2_dev,
 	}
 
 	vdev->fops = &msm_vid_fops;
-	vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE_MPLANE | V4L2_CAP_STREAMING |
-							V4L2_CAP_READWRITE;
+	vdev->device_caps = V4L2_CAP_VIDEO_CAPTURE_MPLANE | V4L2_CAP_STREAMING
+			  | V4L2_CAP_READWRITE | V4L2_CAP_IO_MC;
 	vdev->ioctl_ops = &msm_vid_ioctl_ops;
 	vdev->release = msm_video_release;
 	vdev->v4l2_dev = v4l2_dev;