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| -rw-r--r-- | Documentation/video4linux/soc-camera.txt | 146 |
1 files changed, 75 insertions, 71 deletions
diff --git a/Documentation/video4linux/soc-camera.txt b/Documentation/video4linux/soc-camera.txt index 3f87c7da4ca2..f62fcdbc8b9f 100644 --- a/Documentation/video4linux/soc-camera.txt +++ b/Documentation/video4linux/soc-camera.txt @@ -9,32 +9,36 @@ The following terms are used in this document: 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, + 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 + 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. +The soc-camera subsystem initially provided a unified API between camera host +drivers and camera sensor drivers. Later the soc-camera sensor API has been +replaced with the V4L2 standard subdev API. This also made camera driver re-use +with non-soc-camera hosts possible. The camera host API to the soc-camera core +has been preserved. -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. +Soc-camera implements a V4L2 interface to the user, currently only the "mmap" +method is supported by host drivers. However, the soc-camera core also provides +support for the "read" method. + +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. +As of 3.7 there are seven host drivers in the mainline: atmel-isi.c, +mx1_camera.c (broken, scheduled for removal), mx2_camera.c, mx3_camera.c, +omap1_camera.c, pxa_camera.c, sh_mobile_ceu_camera.c, and multiple sensor +drivers under drivers/media/i2c/soc_camera/. Camera host API --------------- @@ -45,38 +49,37 @@ 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, -}; + struct soc_camera_host *ici; + ici->drv_name = DRV_NAME; + ici->ops = &camera_host_ops; + ici->priv = pcdev; + ici->v4l2_dev.dev = &pdev->dev; + ici->nr = pdev->id; All camera host methods are passed in a struct soc_camera_host_ops: -static struct soc_camera_host_ops pxa_soc_camera_host_ops = { +static struct soc_camera_host_ops 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 = camera_add_device, + .remove = camera_remove_device, + .set_fmt = camera_set_fmt_cap, + .try_fmt = camera_try_fmt_cap, + .init_videobuf2 = camera_init_videobuf2, + .poll = camera_poll, + .querycap = camera_querycap, + .set_bus_param = camera_set_bus_param, + /* The rest of host operations are optional */ }; .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 +from the host. .set_bus_param is used to configure physical connection +parameters between the host and the sensor. .init_videobuf2 is called by +soc-camera core when a video-device is opened, the host driver would typically +call vb2_queue_init() in this method. Further video-buffer management is +implemented completely by the specific camera host driver. If the host driver +supports non-standard pixel format conversion, it should implement a +.get_formats and, possibly, a .put_formats operations. See below for more +details about format conversion. The rest of the methods are called from respective V4L2 operations. Camera API @@ -84,37 +87,21 @@ 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. +and optionally provide platform .power and .reset methods for the camera. This +struct is provided to the camera driver via the I2C client device platform data +and can be obtained, using the soc_camera_i2c_to_link() macro. Care should be +taken, when using soc_camera_vdev_to_subdev() and when accessing struct +soc_camera_device, using v4l2_get_subdev_hostdata(): both only work, when +running on an soc-camera host. The actual camera driver operation is implemented +using the V4L2 subdev API. Additionally soc-camera camera drivers can use +auxiliary soc-camera helper functions like soc_camera_power_on() and +soc_camera_power_off(), which switch regulators, provided by the platform and call +board-specific power switching methods. soc_camera_apply_board_flags() takes +camera bus configuration capability flags and applies any board transformations, +e.g. signal polarity inversion. soc_mbus_get_fmtdesc() can be used to obtain a +pixel format descriptor, corresponding to a certain media-bus pixel format code. +soc_camera_limit_side() can be used to restrict beginning and length of a frame +side, based on camera capabilities. VIDIOC_S_CROP and VIDIOC_S_FMT behaviour ---------------------------------------- @@ -153,8 +140,25 @@ implemented. User window geometry is kept in .user_width and .user_height fields in struct soc_camera_device and used by the soc-camera core and host drivers. The core updates these fields upon successful completion of a .s_fmt() call, but if these -fields change elsewhere, e.g., during .s_crop() processing, the host driver is +fields change elsewhere, e.g. during .s_crop() processing, the host driver is responsible for updating them. +Format conversion +----------------- + +V4L2 distinguishes between pixel formats, as they are stored in memory, and as +they are transferred over a media bus. Soc-camera provides support to +conveniently manage these formats. A table of standard transformations is +maintained by soc-camera core, which describes, what FOURCC pixel format will +be obtained, if a media-bus pixel format is stored in memory according to +certain rules. E.g. if V4L2_MBUS_FMT_YUYV8_2X8 data is sampled with 8 bits per +sample and stored in memory in the little-endian order with no gaps between +bytes, data in memory will represent the V4L2_PIX_FMT_YUYV FOURCC format. These +standard transformations will be used by soc-camera or by camera host drivers to +configure camera drivers to produce the FOURCC format, requested by the user, +using the VIDIOC_S_FMT ioctl(). Apart from those standard format conversions, +host drivers can also provide their own conversion rules by implementing a +.get_formats and, if required, a .put_formats methods. + -- Author: Guennadi Liakhovetski <g.liakhovetski@gmx.de> |