Hi Hans,
On Wed, 2016-02-17 at 08:47 +0100, Hans Verkuil wrote:
> On 02/16/2016 07:37 AM, tiffany lin wrote:
> >>> +static int fops_vcodec_open(struct file *file)
> >>> +{
> >>> + struct video_device *vfd = video_devdata(file);
> >>> + struct mtk_vcodec_dev *dev = video_drvdata(file);
> >>> + struct mtk_vcodec_ctx *ctx = NULL;
> >>> + int ret = 0;
> >>> +
> >>> + mutex_lock(&dev->dev_mutex);
> >>> +
> >>> + ctx = devm_kzalloc(&dev->plat_dev->dev, sizeof(*ctx), GFP_KERNEL);
> >>> + if (!ctx) {
> >>> + ret = -ENOMEM;
> >>> + goto err_alloc;
> >>> + }
> >>> +
> >>> + if (dev->num_instances >= MTK_VCODEC_MAX_ENCODER_INSTANCES) {
> >>> + mtk_v4l2_err("Too many open contexts\n");
> >>> + ret = -EBUSY;
> >>> + goto err_no_ctx;
> >>
> >> Hmm. I never like it if you can't open a video node because of a reason like this.
> >>
> >> I.e. a simple 'v4l2-ctl -D' (i.e. calling QUERYCAP) should never fail.
> >>
> >> If there are hardware limitation that prevent more than X instances from running at
> >> the same time, then those limitations typically kick in when you start to stream
> >> (or possibly when calling REQBUFS). But before that it should always be possible to
> >> open the device.
> >>
> >> Having this check at open() is an indication of a poor design.
> >>
> >> Is this is a hardware limitation at all?
> >>
> > This is to make sure performance meet requirements, such as bitrate and
> > framerate.
>
> Is it the driver's job to make enforce this? What if the application only
> deals with low-res video, but wants to encode a lot of those? Or is encoding
> a video off-line?
>
> The driver generally doesn't know the use-case, so if this is an artificial
> limitation as opposed to a hardware limitation, then I would just drop this.
>
We got your point, we will remove this artificial limitation in next
version.
best regards,
Tiffany
> Regards,
>
> Hans
>
> > We got your point. We will remove this and move limitation control to
> > start_streaming or REQBUFS.
> > Appreciated for your suggestion.:)
> >
> >
> >>> + }
>
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