linux-kernel - Re: [PATCH v7 2/7] drivers:media:radio: wl128x: fmdrv

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Date:	Sat, 18 Dec 2010 12:38:55 +0100
From:	Hans Verkuil <hverkuil@...all.nl>
To:	manjunatha_halli@...com
Cc:	mchehab@...radead.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org
Subject: Re: [PATCH v7 2/7] drivers:media:radio: wl128x: fmdrv_v4l2 sources

On Friday, December 17, 2010 12:06:31 manjunatha_halli@...com wrote:
> From: Manjunatha Halli <manjunatha_halli@...com>
> 
> This module interfaces V4L2 subsystem and FM common module.
> It registers itself with V4L2 as Radio module.
> 
> Signed-off-by: Manjunatha Halli <manjunatha_halli@...com>
> ---
>  drivers/media/radio/wl128x/fmdrv_v4l2.c |  588 +++++++++++++++++++++++++++++++
>  drivers/media/radio/wl128x/fmdrv_v4l2.h |   33 ++
>  2 files changed, 621 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/media/radio/wl128x/fmdrv_v4l2.c
>  create mode 100644 drivers/media/radio/wl128x/fmdrv_v4l2.h
> 
> diff --git a/drivers/media/radio/wl128x/fmdrv_v4l2.c b/drivers/media/radio/wl128x/fmdrv_v4l2.c
> new file mode 100644
> index 0000000..623102f
> --- /dev/null
> +++ b/drivers/media/radio/wl128x/fmdrv_v4l2.c

<snip>

> +static const struct v4l2_file_operations fm_drv_fops = {
> +	.owner = THIS_MODULE,
> +	.read = fm_v4l2_fops_read,
> +	.write = fm_v4l2_fops_write,
> +	.poll = fm_v4l2_fops_poll,
> +	.ioctl = video_ioctl2,

Please use unlocked_ioctl. The .ioctl call is deprecated since it relied on the
Big Kernel Lock which is in the process of being removed from the kernel. The
BKL serialized all ioctl calls, unlocked_ioctl relies on the driver to serialize
where necessary.

There are two ways of doing the conversion: one is to do all the locking within
the driver, the other is to use core-assisted locking. How to do the core-assisted
locking is described in Documentation/video4linux/v4l2-framework.txt, but I'll
repeat the relevant part here:

v4l2_file_operations and locking
--------------------------------

You can set a pointer to a mutex_lock in struct video_device. Usually this
will be either a top-level mutex or a mutex per device node. If you want
finer-grained locking then you have to set it to NULL and do you own locking.

If a lock is specified then all file operations will be serialized on that
lock. If you use videobuf then you must pass the same lock to the videobuf
queue initialize function: if videobuf has to wait for a frame to arrive, then
it will temporarily unlock the lock and relock it afterwards. If your driver
also waits in the code, then you should do the same to allow other processes
to access the device node while the first process is waiting for something.

The implementation of a hotplug disconnect should also take the lock before
calling v4l2_device_disconnect.

> +	.open = fm_v4l2_fops_open,
> +	.release = fm_v4l2_fops_release,
> +};

Regards,

	Hans

-- 
Hans Verkuil - video4linux developer - sponsored by Cisco
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