[PATCH 2/3] media: coda: Add driver for Coda video codec.

On 9 July 2012 10:19, Philipp Zabel [off-list ref] wrote:

Am Montag, den 09.07.2012, 10:07 +0200 schrieb javier Martin:
[...]

quoted

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+static int vidioc_s_parm(struct file *file, void *priv, struct v4l2_streamparm *a)
+{
+     struct coda_ctx *ctx = fh_to_ctx(priv);
+
+     if (a->type == V4L2_BUF_TYPE_VIDEO_OUTPUT) {
+             if (a->parm.output.timeperframe.numerator != 1) {
+                     v4l2_err(&ctx->dev->v4l2_dev,
+                              "FPS numerator must be 1\n");
+                     return -EINVAL;
+             }
+             ctx->params.framerate =
+                                     a->parm.output.timeperframe.denominator;
+     } else {
+             v4l2_err(&ctx->dev->v4l2_dev,
+                      "Setting FPS is only possible for the output queue\n");
+             return -EINVAL;

Why disallow setting timeperframe on the capture side? Shouldn't it
rather succeed without setting anything and return the current context's
frame rate instead?

quoted

+     }
+     return 0;
+}
+
+static int vidioc_g_parm(struct file *file, void *priv, struct v4l2_streamparm *a)
+{
+     struct coda_ctx *ctx = fh_to_ctx(priv);
+
+     if (a->type == V4L2_BUF_TYPE_VIDEO_OUTPUT) {
+             a->parm.output.timeperframe.denominator =
+                                     ctx->params.framerate;
+             a->parm.output.timeperframe.numerator = 1;
+     } else {
+             v4l2_err(&ctx->dev->v4l2_dev,
+                      "Getting FPS is only possible for the output queue\n");

The nominal capture side timeperframe should match that of the output
side.

Actually, I'm not sure if this needs to be implemented at all, since
V4L2_CAP_TIMEPERFRAME is not set and capture frame dropping / output
frame duplication is not supported.

I am just following the steps of Samsung here:

http://lxr.linux.no/#linux+v3.4.4/drivers/media/video/s5p-mfc/s5p_mfc_enc.c#L1439
http://lxr.linux.no/#linux+v3.4.4/drivers/media/video/s5p-mfc/s5p_mfc_opr.c#L775

I don't think this is completely correct either. According to the V4L2
spec, setting timeperframe from an application is meant to make the
driver skip or duplicate frames to save bandwidth:

http://v4l2spec.bytesex.org/spec-single/v4l2.html#VIDIOC-G-PARM

So returning -EINVAL is not necessarily incorrect, as we can choose not
to support this ioctl - but claiming support for the output side (and
then doing nothing) but returning an error on the capture side seems a
bit inconsistent to me.

I'll remove it since we don't use it either way.

-- 
Javier Martin
Vista Silicon S.L.
CDTUC - FASE C - Oficina S-345
Avda de los Castros s/n
39005- Santander. Cantabria. Spain
+34 942 25 32 60
www.vista-silicon.com