[media] s5p-fimc: Add driver documentation
Add short documentation providing the driver usage details. Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Sylwester Nawrocki
Mauro Carvalho Chehab
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Samsung S5P/EXYNOS4 FIMC driver
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Copyright (C) 2012 Samsung Electronics Co., Ltd.
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---------------------------------------------------------------------------
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The FIMC (Fully Interactive Mobile Camera) device available in Samsung
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SoC Application Processors is an integrated camera host interface, color
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space converter, image resizer and rotator. It's also capable of capturing
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data from LCD controller (FIMD) through the SoC internal writeback data
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path. There are multiple FIMC instances in the SoCs (up to 4), having
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slightly different capabilities, like pixel alignment constraints, rotator
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availability, LCD writeback support, etc. The driver is located at
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drivers/media/video/s5p-fimc directory.
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1. Supported SoCs
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=================
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S5PC100 (mem-to-mem only), S5PV210, EXYNOS4210
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2. Supported features
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=====================
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- camera parallel interface capture (ITU-R.BT601/565);
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- camera serial interface capture (MIPI-CSI2);
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- memory-to-memory processing (color space conversion, scaling, mirror
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and rotation);
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- dynamic pipeline re-configuration at runtime (re-attachment of any FIMC
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instance to any parallel video input or any MIPI-CSI front-end);
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- runtime PM and system wide suspend/resume
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Not currently supported:
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- LCD writeback input
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- per frame clock gating (mem-to-mem)
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3. Files partitioning
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=====================
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- media device driver
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drivers/media/video/s5p-fimc/fimc-mdevice.[ch]
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- camera capture video device driver
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drivers/media/video/s5p-fimc/fimc-capture.c
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- MIPI-CSI2 receiver subdev
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drivers/media/video/s5p-fimc/mipi-csis.[ch]
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- video post-processor (mem-to-mem)
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drivers/media/video/s5p-fimc/fimc-core.c
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- common files
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drivers/media/video/s5p-fimc/fimc-core.h
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drivers/media/video/s5p-fimc/fimc-reg.h
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drivers/media/video/s5p-fimc/regs-fimc.h
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4. User space interfaces
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========================
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4.1. Media device interface
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The driver supports Media Controller API as defined at
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http://http://linuxtv.org/downloads/v4l-dvb-apis/media_common.html
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The media device driver name is "SAMSUNG S5P FIMC".
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The purpose of this interface is to allow changing assignment of FIMC instances
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to the SoC peripheral camera input at runtime and optionally to control internal
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connections of the MIPI-CSIS device(s) to the FIMC entities.
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The media device interface allows to configure the SoC for capturing image
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data from the sensor through more than one FIMC instance (e.g. for simultaneous
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viewfinder and still capture setup).
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Reconfiguration is done by enabling/disabling media links created by the driver
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during initialization. The internal device topology can be easily discovered
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through media entity and links enumeration.
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4.2. Memory-to-memory video node
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V4L2 memory-to-memory interface at /dev/video? device node. This is standalone
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video device, it has no media pads. However please note the mem-to-mem and
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capture video node operation on same FIMC instance is not allowed. The driver
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detects such cases but the applications should prevent them to avoid an
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undefined behaviour.
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4.3. Capture video node
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The driver supports V4L2 Video Capture Interface as defined at:
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http://linuxtv.org/downloads/v4l-dvb-apis/devices.html
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At the capture and mem-to-mem video nodes only the multi-planar API is
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supported. For more details see:
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http://linuxtv.org/downloads/v4l-dvb-apis/planar-apis.html
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4.4. Camera capture subdevs
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Each FIMC instance exports a sub-device node (/dev/v4l-subdev?), a sub-device
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node is also created per each available and enabled at the platform level
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MIPI-CSI receiver device (currently up to two).
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4.5. sysfs
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In order to enable more precise camera pipeline control through the sub-device
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API the driver creates a sysfs entry associated with "s5p-fimc-md" platform
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device. The entry path is: /sys/platform/devices/s5p-fimc-md/subdev_conf_mode.
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In typical use case there could be a following capture pipeline configuration:
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sensor subdev -> mipi-csi subdev -> fimc subdev -> video node
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When we configure these devices through sub-device API at user space, the
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configuration flow must be from left to right, and the video node is
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configured as last one.
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When we don't use sub-device user space API the whole configuration of all
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devices belonging to the pipeline is done at the video node driver.
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The sysfs entry allows to instruct the capture node driver not to configure
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the sub-devices (format, crop), to avoid resetting the subdevs' configuration
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when the last configuration steps at the video node is performed.
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For full sub-device control support (subdevs configured at user space before
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starting streaming):
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# echo "sub-dev" > /sys/platform/devices/s5p-fimc-md/subdev_conf_mode
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For V4L2 video node control only (subdevs configured internally by the host
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driver):
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# echo "vid-dev" > /sys/platform/devices/s5p-fimc-md/subdev_conf_mode
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This is a default option.
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5. Device mapping to video and subdev device nodes
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==================================================
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There are associated two video device nodes with each device instance in
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hardware - video capture and mem-to-mem and additionally a subdev node for
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more precise FIMC capture subsystem control. In addition a separate v4l2
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sub-device node is created per each MIPI-CSIS device.
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How to find out which /dev/video? or /dev/v4l-subdev? is assigned to which
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device?
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You can either grep through the kernel log to find relevant information, i.e.
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# dmesg | grep -i fimc
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(note that udev, if present, might still have rearranged the video nodes),
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or retrieve the information from /dev/media? with help of the media-ctl tool:
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# media-ctl -p
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6. Platform support
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===================
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The machine code (plat-s5p and arch/arm/mach-*) must select following options
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CONFIG_S5P_DEV_FIMC0 mandatory
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CONFIG_S5P_DEV_FIMC1 \
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CONFIG_S5P_DEV_FIMC2 | optional
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CONFIG_S5P_DEV_FIMC3 |
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CONFIG_S5P_SETUP_FIMC /
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CONFIG_S5P_SETUP_MIPIPHY \
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CONFIG_S5P_DEV_CSIS0 | optional for MIPI-CSI interface
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CONFIG_S5P_DEV_CSIS1 /
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Except that, relevant s5p_device_fimc? should be registered in the machine code
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in addition to a "s5p-fimc-md" platform device to which the media device driver
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is bound. The "s5p-fimc-md" device instance is required even if only mem-to-mem
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operation is used.
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The description of sensor(s) attached to FIMC/MIPI-CSIS camera inputs should be
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passed as the "s5p-fimc-md" device platform_data. The platform data structure
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is defined in file include/media/s5p_fimc.h.
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7. Build
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========
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This driver depends on following config options:
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PLAT_S5P,
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PM_RUNTIME,
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I2C,
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REGULATOR,
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VIDEO_V4L2_SUBDEV_API,
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If the driver is built as a loadable kernel module (CONFIG_VIDEO_SAMSUNG_S5P_FIMC=m)
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two modules are created (in addition to the core v4l2 modules): s5p-fimc.ko and
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optional s5p-csis.ko (MIPI-CSI receiver subdev).
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