Hi Akinobu,
On 05/27/2018 05:30 PM, Akinobu Mita wrote:
> The open() operation for the pxa_camera driver always calls s_power()
> operation to put its subdevice sensor in normal operation mode, and the
> release() operation always call s_power() operation to put the subdevice
> in power saving mode.
>
> This requires the subdevice sensor driver to keep track of its power
> state in order to avoid putting the subdevice in power saving mode while
> the device is still opened by some users.
>
> Many subdevice drivers handle it by the boilerplate code that increments
> and decrements an internal counter in s_power() like below:
>
> /*
> * If the power count is modified from 0 to != 0 or from != 0 to 0,
> * update the power state.
> */
> if (sensor->power_count == !on) {
> ret = ov5640_set_power(sensor, !!on);
> if (ret)
> goto out;
> }
>
> /* Update the power count. */
> sensor->power_count += on ? 1 : -1;
>
> However, some subdevice drivers don't handle it and may cause a problem
> with the pxa_camera driver if the video device is opened by more than
> two users at the same time.
>
> Instead of propagating the boilerplate code for each subdevice driver
> that implement s_power, this introduces an trick that many V4L2 drivers
> are using with v4l2_fh_is_singular_file().
>
> Cc: Sakari Ailus <sakari.ai...@linux.intel.com>
> Cc: Mauro Carvalho Chehab <mche...@kernel.org>
> Signed-off-by: Akinobu Mita <akinobu.m...@gmail.com>
> ---
> * v2
> - Print warning message when s_power() is failed. (not printing warning
> when _vb2_fop_release() is failed as it always returns zero for now)
Please note that v1 has already been merged, so if you can make a v3 rebased
on top of the latest media_tree master branch, then I'll queue that up for
4.18.
Regards,
Hans
>
> drivers/media/platform/pxa_camera.c | 23 ++++++++++++++++++-----
> 1 file changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/media/platform/pxa_camera.c
> b/drivers/media/platform/pxa_camera.c
> index c71a007..a35f461 100644
> --- a/drivers/media/platform/pxa_camera.c
> +++ b/drivers/media/platform/pxa_camera.c
> @@ -2040,6 +2040,9 @@ static int pxac_fops_camera_open(struct file *filp)
> if (ret < 0)
> goto out;
>
> + if (!v4l2_fh_is_singular_file(filp))
> + goto out;
> +
> ret = sensor_call(pcdev, core, s_power, 1);
> if (ret)
> v4l2_fh_release(filp);
> @@ -2052,13 +2055,23 @@ static int pxac_fops_camera_release(struct file *filp)
> {
> struct pxa_camera_dev *pcdev = video_drvdata(filp);
> int ret;
> -
> - ret = vb2_fop_release(filp);
> - if (ret < 0)
> - return ret;
> + bool fh_singular;
>
> mutex_lock(&pcdev->mlock);
> - ret = sensor_call(pcdev, core, s_power, 0);
> +
> + fh_singular = v4l2_fh_is_singular_file(filp);
> +
> + ret = _vb2_fop_release(filp, NULL);
> +
> + if (fh_singular) {
> + ret = sensor_call(pcdev, core, s_power, 0);
> + if (ret) {
> + dev_warn(pcdev_to_dev(pcdev),
> + "Failed to put subdevice in power saving mode:
> %d\n",
> + ret);
> + }
> + }
> +
> mutex_unlock(&pcdev->mlock);
>
> return ret;
>
