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SubjectRe: [RFC PATCH v1 6/7] media: video: introduce face detection driver module
Hi Ming,

On 12/02/2011 04:02 PM, Ming Lei wrote:
> This patch introduces one driver for face detection purpose.
>
> The driver is responsible for all v4l2 stuff, buffer management
> and other general things, and doesn't touch face detection hardware
> directly. Several interfaces are exported to low level drivers
> (such as the coming omap4 FD driver)which will communicate with
> face detection hw module.
>
> So the driver will make driving face detection hw modules more
> easy.
>
> TODO:
> - implement FD setting interfaces with v4l2 controls or
> ext controls
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
...
> +static int vidioc_g_fd_result(struct file *file, void *priv,
> + struct v4l2_fd_result *f)
> +{
> + struct fdif_dev *dev = video_drvdata(file);
> + unsigned long flags;
> + struct v4l2_fdif_result *tmp;
> + struct v4l2_fdif_result *fr = NULL;
> + unsigned int cnt = 0;
> + int ret = -EINVAL;
> +
> + spin_lock_irqsave(&dev->lock, flags);
> + list_for_each_entry(tmp, &dev->fdif_dq.complete, list)
> + if (tmp->index == f->buf_index) {
> + fr = tmp;
> + list_del(&tmp->list);
> + break;
> + }
> + spin_unlock_irqrestore(&dev->lock, flags);
> +
> + if (fr) {
> + ret = 0;
> + cnt = min(f->face_cnt, fr->face_cnt);
> + if (cnt)
> + memcpy(f->fd, fr->faces,
> + sizeof(struct v4l2_fd_detection) * cnt);
> + f->face_cnt = cnt;
> + kfree(fr->faces);
> + kfree(fr);

struct v4l2_fdif_result is allocated in HW driver at the time when FD result
is read out and it is freed in generic module here. Not sure if it is a good
practice to split memory management like this. Also IMHO it would be much
better to pre-allocate memory for FD output data, according to maximum number
of detected faces per frame. It could be more reliable than allocating memory
in interrupt context per each frame.


> + }
> + return ret;
> +}

--
Regards,
Sylwester


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