You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
120 lines
4.7 KiB
120 lines
4.7 KiB
Soc-Camera Subsystem
|
|
====================
|
|
|
|
Terminology
|
|
-----------
|
|
|
|
The following terms are used in this document:
|
|
- camera / camera device / camera sensor - a video-camera sensor chip, capable
|
|
of connecting to a variety of systems and interfaces, typically uses i2c for
|
|
control and configuration, and a parallel or a serial bus for data.
|
|
- camera host - an interface, to which a camera is connected. Typically a
|
|
specialised interface, present on many SoCs, e.g., PXA27x and PXA3xx, SuperH,
|
|
AVR32, i.MX27, i.MX31.
|
|
- camera host bus - a connection between a camera host and a camera. Can be
|
|
parallel or serial, consists of data and control lines, e.g., clock, vertical
|
|
and horizontal synchronization signals.
|
|
|
|
Purpose of the soc-camera subsystem
|
|
-----------------------------------
|
|
|
|
The soc-camera subsystem provides a unified API between camera host drivers and
|
|
camera sensor drivers. It implements a V4L2 interface to the user, currently
|
|
only the mmap method is supported.
|
|
|
|
This subsystem has been written to connect drivers for System-on-Chip (SoC)
|
|
video capture interfaces with drivers for CMOS camera sensor chips to enable
|
|
the reuse of sensor drivers with various hosts. The subsystem has been designed
|
|
to support multiple camera host interfaces and multiple cameras per interface,
|
|
although most applications have only one camera sensor.
|
|
|
|
Existing drivers
|
|
----------------
|
|
|
|
As of 2.6.27-rc4 there are two host drivers in the mainline: pxa_camera.c for
|
|
PXA27x SoCs and sh_mobile_ceu_camera.c for SuperH SoCs, and four sensor drivers:
|
|
mt9m001.c, mt9m111.c, mt9v022.c and a generic soc_camera_platform.c driver. This
|
|
list is not supposed to be updated, look for more examples in your tree.
|
|
|
|
Camera host API
|
|
---------------
|
|
|
|
A host camera driver is registered using the
|
|
|
|
soc_camera_host_register(struct soc_camera_host *);
|
|
|
|
function. The host object can be initialized as follows:
|
|
|
|
static struct soc_camera_host pxa_soc_camera_host = {
|
|
.drv_name = PXA_CAM_DRV_NAME,
|
|
.ops = &pxa_soc_camera_host_ops,
|
|
};
|
|
|
|
All camera host methods are passed in a struct soc_camera_host_ops:
|
|
|
|
static struct soc_camera_host_ops pxa_soc_camera_host_ops = {
|
|
.owner = THIS_MODULE,
|
|
.add = pxa_camera_add_device,
|
|
.remove = pxa_camera_remove_device,
|
|
.suspend = pxa_camera_suspend,
|
|
.resume = pxa_camera_resume,
|
|
.set_fmt_cap = pxa_camera_set_fmt_cap,
|
|
.try_fmt_cap = pxa_camera_try_fmt_cap,
|
|
.init_videobuf = pxa_camera_init_videobuf,
|
|
.reqbufs = pxa_camera_reqbufs,
|
|
.poll = pxa_camera_poll,
|
|
.querycap = pxa_camera_querycap,
|
|
.try_bus_param = pxa_camera_try_bus_param,
|
|
.set_bus_param = pxa_camera_set_bus_param,
|
|
};
|
|
|
|
.add and .remove methods are called when a sensor is attached to or detached
|
|
from the host, apart from performing host-internal tasks they shall also call
|
|
sensor driver's .init and .release methods respectively. .suspend and .resume
|
|
methods implement host's power-management functionality and its their
|
|
responsibility to call respective sensor's methods. .try_bus_param and
|
|
.set_bus_param are used to negotiate physical connection parameters between the
|
|
host and the sensor. .init_videobuf is called by soc-camera core when a
|
|
video-device is opened, further video-buffer management is implemented completely
|
|
by the specific camera host driver. The rest of the methods are called from
|
|
respective V4L2 operations.
|
|
|
|
Camera API
|
|
----------
|
|
|
|
Sensor drivers can use struct soc_camera_link, typically provided by the
|
|
platform, and used to specify to which camera host bus the sensor is connected,
|
|
and arbitrarily provide platform .power and .reset methods for the camera.
|
|
soc_camera_device_register() and soc_camera_device_unregister() functions are
|
|
used to add a sensor driver to or remove one from the system. The registration
|
|
function takes a pointer to struct soc_camera_device as the only parameter.
|
|
This struct can be initialized as follows:
|
|
|
|
/* link to driver operations */
|
|
icd->ops = &mt9m001_ops;
|
|
/* link to the underlying physical (e.g., i2c) device */
|
|
icd->control = &client->dev;
|
|
/* window geometry */
|
|
icd->x_min = 20;
|
|
icd->y_min = 12;
|
|
icd->x_current = 20;
|
|
icd->y_current = 12;
|
|
icd->width_min = 48;
|
|
icd->width_max = 1280;
|
|
icd->height_min = 32;
|
|
icd->height_max = 1024;
|
|
icd->y_skip_top = 1;
|
|
/* camera bus ID, typically obtained from platform data */
|
|
icd->iface = icl->bus_id;
|
|
|
|
struct soc_camera_ops provides .probe and .remove methods, which are called by
|
|
the soc-camera core, when a camera is matched against or removed from a camera
|
|
host bus, .init, .release, .suspend, and .resume are called from the camera host
|
|
driver as discussed above. Other members of this struct provide respective V4L2
|
|
functionality.
|
|
|
|
struct soc_camera_device also links to an array of struct soc_camera_data_format,
|
|
listing pixel formats, supported by the camera.
|
|
|
|
--
|
|
Author: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
|
|
|