From mboxrd@z Thu Jan  1 00:00:00 1970
From: javier.martin@vista-silicon.com (javier Martin)
Date: Mon, 9 Jul 2012 10:21:44 +0200
Subject: [PATCH 2/3] media: coda: Add driver for Coda video codec.
In-Reply-To: <1341821944.2489.16.camel@pizza.hi.pengutronix.de>
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 <1341816350.2489.1.camel@pizza.hi.pengutronix.de>
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To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 9 July 2012 10:19, Philipp Zabel <p.zabel@pengutronix.de> wrote:
> Am Montag, den 09.07.2012, 10:07 +0200 schrieb javier Martin:
> [...]
>> >> +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?
>> >
>> >> +     }
>> >> +     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.
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