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Date: Wed, 08 Jan 2014 22:19:01 +0100
From: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
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To: m silverstri <michael.j.silverstri@gmail.com>
CC: Devin Heitmueller <dheitmueller@kernellabs.com>,
	linux-media <linux-media@vger.kernel.org>
Subject: Re: How can I find out what is the driver for device node '/dev/video11'
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On 01/08/2014 08:15 PM, m silverstri wrote:
> Thanks.
>
> I am studying android source code.
>  From here,  it has code which open("/dev/video11", O_RDWR, 0) as
> decoding device.
>
> http://androidxref.com/4.4.2_r1/xref/hardware/samsung_slsi/exynos5/libhwjpeg/ExynosJpegBase.cpp

What you're looking for might be this proprietary Samsung JPEG codec driver
used in Android.

https://android.googlesource.com/kernel/exynos/+/android-exynos-3.4/drivers/media/video/exynos/jpeg/

If you intend to use mainline kernel you need to consider the s5p-jpeg 
driver,
which exposes to user space standard interface without any proprietary 
additions
incompatible with the V4L2 spec.

> I want to find out which is the corresponding driver code for device
> '/dev/video11'.

I suspect these numbers are fixed in the Android kernel (they are hard
coded in the user space library as you're pointing out above), which is
a pretty bad practice.

It's better to use VIDIOC_QUERYCAP ioctl to find a video device with
specific name, as Devin suggested. You can also find a video device
exposed by a specific driver through sysfs, as is done in
exynos_v4l2_open_devname() function in this a bit less hacky code:

https://android.googlesource.com/platform/hardware/samsung_slsi/exynos5/+/jb-mr1-release/libv4l2/exynos_v4l2.c

Thanks,
Sylwester