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android_kernel_xiaomi_sm8350/Documentation/usb/et61x251.txt
Luca Risolia 7ce08c93e3 [PATCH] USB: Add ET61X[12]51 Video4Linux2 driver 
This patch adds a Video4Linux2 driver giving support
to ET61X151 and ET61X251 PC Camera Controllers made by
Etoms Electronics.

Signed-off-by: Luca Risolia <luca.risolia@studio.unibo.it>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2006-01-31 17:23:39 -08:00

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ET61X[12]51 PC Camera Controllers
Driver for Linux
=================================
- Documentation -
Index
=====
1. Copyright
2. Disclaimer
3. License
4. Overview and features
5. Module dependencies
6. Module loading
7. Module parameters
8. Optional device control through "sysfs"
9. Supported devices
10. Notes for V4L2 application developers
11. Contact information
1. Copyright
============
Copyright (C) 2006 by Luca Risolia <luca.risolia@studio.unibo.it>
2. Disclaimer
=============
Etoms is a trademark of Etoms Electronics Corp.
This software is not developed or sponsored by Etoms Electronics.
3. License
==========
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
4. Overview and features
========================
This driver supports the video interface of the devices mounting the ET61X151
or ET61X251 PC Camera Controllers.
It's worth to note that Etoms Electronics has never collaborated with the
author during the development of this project; despite several requests,
Etoms Electronics also refused to release enough detailed specifications of
the video compression engine.
The driver relies on the Video4Linux2 and USB core modules. It has been
designed to run properly on SMP systems as well.
The latest version of the ET61X[12]51 driver can be found at the following URL:
http://www.linux-projects.org/
Some of the features of the driver are:
- full compliance with the Video4Linux2 API (see also "Notes for V4L2
application developers" paragraph);
- available mmap or read/poll methods for video streaming through isochronous
data transfers;
- automatic detection of image sensor;
- support for any window resolutions and optional panning within the maximum
pixel area of image sensor;
- image downscaling with arbitrary scaling factors from 1 and 2 in both
directions (see "Notes for V4L2 application developers" paragraph);
- two different video formats for uncompressed or compressed data in low or
high compression quality (see also "Notes for V4L2 application developers"
paragraph);
- full support for the capabilities of every possible image sensors that can
be connected to the ET61X[12]51 bridges, including, for istance, red, green,
blue and global gain adjustments and exposure control (see "Supported
devices" paragraph for details);
- use of default color settings for sunlight conditions;
- dynamic I/O interface for both ET61X[12]51 and image sensor control (see
"Optional device control through 'sysfs'" paragraph);
- dynamic driver control thanks to various module parameters (see "Module
parameters" paragraph);
- up to 64 cameras can be handled at the same time; they can be connected and
disconnected from the host many times without turning off the computer, if
the system supports hotplugging;
- no known bugs.
5. Module dependencies
======================
For it to work properly, the driver needs kernel support for Video4Linux and
USB.
The following options of the kernel configuration file must be enabled and
corresponding modules must be compiled:
# Multimedia devices
#
CONFIG_VIDEO_DEV=m
To enable advanced debugging functionality on the device through /sysfs:
# Multimedia devices
#
CONFIG_VIDEO_ADV_DEBUG=y
# USB support
#
CONFIG_USB=m
In addition, depending on the hardware being used, the modules below are
necessary:
# USB Host Controller Drivers
#
CONFIG_USB_EHCI_HCD=m
CONFIG_USB_UHCI_HCD=m
CONFIG_USB_OHCI_HCD=m
And finally:
# USB Multimedia devices
#
CONFIG_USB_ET61X251=m
6. Module loading
=================
To use the driver, it is necessary to load the "et61x251" module into memory
after every other module required: "videodev", "usbcore" and, depending on
the USB host controller you have, "ehci-hcd", "uhci-hcd" or "ohci-hcd".
Loading can be done as shown below:
[root@localhost home]# modprobe et61x251
At this point the devices should be recognized. You can invoke "dmesg" to
analyze kernel messages and verify that the loading process has gone well:
[user@localhost home]$ dmesg
7. Module parameters
====================
Module parameters are listed below:
-------------------------------------------------------------------------------
Name: video_nr
Type: short array (min = 0, max = 64)
Syntax: <-1|n[,...]>
Description: Specify V4L2 minor mode number:
-1 = use next available
n = use minor number n
You can specify up to 64 cameras this way.
For example:
video_nr=-1,2,-1 would assign minor number 2 to the second
registered camera and use auto for the first one and for every
other camera.
Default: -1
-------------------------------------------------------------------------------
Name: force_munmap
Type: bool array (min = 0, max = 64)
Syntax: <0|1[,...]>
Description: Force the application to unmap previously mapped buffer memory
before calling any VIDIOC_S_CROP or VIDIOC_S_FMT ioctl's. Not
all the applications support this feature. This parameter is
specific for each detected camera.
0 = do not force memory unmapping
1 = force memory unmapping (save memory)
Default: 0
-------------------------------------------------------------------------------
Name: debug
Type: ushort
Syntax: <n>
Description: Debugging information level, from 0 to 3:
0 = none (use carefully)
1 = critical errors
2 = significant informations
3 = more verbose messages
Level 3 is useful for testing only, when only one device
is used at the same time. It also shows some more informations
about the hardware being detected. This module parameter can be
changed at runtime thanks to the /sys filesystem interface.
Default: 2
-------------------------------------------------------------------------------
8. Optional device control through "sysfs"
==========================================
If the kernel has been compiled with the CONFIG_VIDEO_ADV_DEBUG option enabled,
it is possible to read and write both the ET61X[12]51 and the image sensor
registers by using the "sysfs" filesystem interface.
There are four files in the /sys/class/video4linux/videoX directory for each
registered camera: "reg", "val", "i2c_reg" and "i2c_val". The first two files
control the ET61X[12]51 bridge, while the other two control the sensor chip.
"reg" and "i2c_reg" hold the values of the current register index where the
following reading/writing operations are addressed at through "val" and
"i2c_val". Their use is not intended for end-users, unless you know what you
are doing. Remember that you must be logged in as root before writing to them.
As an example, suppose we were to want to read the value contained in the
register number 1 of the sensor register table - which is usually the product
identifier - of the camera registered as "/dev/video0":
[root@localhost #] cd /sys/class/video4linux/video0
[root@localhost #] echo 1 > i2c_reg
[root@localhost #] cat i2c_val
Note that if the sensor registers can not be read, "cat" will fail.
To avoid race conditions, all the I/O accesses to the files are serialized.
9. Supported devices
====================
None of the names of the companies as well as their products will be mentioned
here. They have never collaborated with the author, so no advertising.
From the point of view of a driver, what unambiguously identify a device are
its vendor and product USB identifiers. Below is a list of known identifiers of
devices mounting the ET61X[12]51 PC camera controllers:
Vendor ID Product ID
--------- ----------
0x102c 0x6151
0x102c 0x6251
0x102c 0x6253
0x102c 0x6254
0x102c 0x6255
0x102c 0x6256
0x102c 0x6257
0x102c 0x6258
0x102c 0x6259
0x102c 0x625a
0x102c 0x625b
0x102c 0x625c
0x102c 0x625d
0x102c 0x625e
0x102c 0x625f
0x102c 0x6260
0x102c 0x6261
0x102c 0x6262
0x102c 0x6263
0x102c 0x6264
0x102c 0x6265
0x102c 0x6266
0x102c 0x6267
0x102c 0x6268
0x102c 0x6269
The following image sensors are supported:
Model Manufacturer
----- ------------
TAS5130D1B Taiwan Advanced Sensor Corporation
All the available control settings of each image sensor are supported through
the V4L2 interface.
10. Notes for V4L2 application developers
========================================
This driver follows the V4L2 API specifications. In particular, it enforces two
rules:
- exactly one I/O method, either "mmap" or "read", is associated with each
file descriptor. Once it is selected, the application must close and reopen the
device to switch to the other I/O method;
- although it is not mandatory, previously mapped buffer memory should always
be unmapped before calling any "VIDIOC_S_CROP" or "VIDIOC_S_FMT" ioctl's.
The same number of buffers as before will be allocated again to match the size
of the new video frames, so you have to map the buffers again before any I/O
attempts on them.
Consistently with the hardware limits, this driver also supports image
downscaling with arbitrary scaling factors from 1 and 2 in both directions.
However, the V4L2 API specifications don't correctly define how the scaling
factor can be chosen arbitrarily by the "negotiation" of the "source" and
"target" rectangles. To work around this flaw, we have added the convention
that, during the negotiation, whenever the "VIDIOC_S_CROP" ioctl is issued, the
scaling factor is restored to 1.
This driver supports two different video formats: the first one is the "8-bit
Sequential Bayer" format and can be used to obtain uncompressed video data
from the device through the current I/O method, while the second one provides
"raw" compressed video data (without frame headers not related to the
compressed data). The current compression quality may vary from 0 to 1 and can
be selected or queried thanks to the VIDIOC_S_JPEGCOMP and VIDIOC_G_JPEGCOMP
V4L2 ioctl's.
11. Contact information
=======================
The author may be contacted by e-mail at <luca.risolia@studio.unibo.it>.
GPG/PGP encrypted e-mail's are accepted. The GPG key ID of the author is
'FCE635A4'; the public 1024-bit key should be available at any keyserver;
the fingerprint is: '88E8 F32F 7244 68BA 3958 5D40 99DA 5D2A FCE6 35A4'.
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