[media] omap3isp: Add documentation
Add documentation on the OMAP 3 ISP driver. Document the subdevs, V4L2 events and private IOCTLs the driver implements Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Signed-off-by: David Cohen <dacohen@gmail.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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Sakari Ailus
Mauro Carvalho Chehab
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OMAP 3 Image Signal Processor (ISP) driver
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Copyright (C) 2010 Nokia Corporation
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Copyright (C) 2009 Texas Instruments, Inc.
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Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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Sakari Ailus <sakari.ailus@iki.fi>
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David Cohen <dacohen@gmail.com>
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Introduction
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============
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This file documents the Texas Instruments OMAP 3 Image Signal Processor (ISP)
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driver located under drivers/media/video/omap3isp. The original driver was
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written by Texas Instruments but since that it has been rewritten (twice) at
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Nokia.
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The driver has been successfully used on the following versions of OMAP 3:
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3430
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3530
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3630
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The driver implements V4L2, Media controller and v4l2_subdev interfaces.
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Sensor, lens and flash drivers using the v4l2_subdev interface in the kernel
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are supported.
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Split to subdevs
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================
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The OMAP 3 ISP is split into V4L2 subdevs, each of the blocks inside the ISP
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having one subdev to represent it. Each of the subdevs provide a V4L2 subdev
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interface to userspace.
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OMAP3 ISP CCP2
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OMAP3 ISP CSI2a
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OMAP3 ISP CCDC
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OMAP3 ISP preview
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OMAP3 ISP resizer
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OMAP3 ISP AEWB
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OMAP3 ISP AF
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OMAP3 ISP histogram
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Each possible link in the ISP is modelled by a link in the Media controller
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interface. For an example program see [2].
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Controlling the OMAP 3 ISP
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==========================
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In general, the settings given to the OMAP 3 ISP take effect at the beginning
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of the following frame. This is done when the module becomes idle during the
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vertical blanking period on the sensor. In memory-to-memory operation the pipe
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is run one frame at a time. Applying the settings is done between the frames.
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All the blocks in the ISP, excluding the CSI-2 and possibly the CCP2 receiver,
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insist on receiving complete frames. Sensors must thus never send the ISP
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partial frames.
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Autoidle does have issues with some ISP blocks on the 3430, at least.
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Autoidle is only enabled on 3630 when the omap3isp module parameter autoidle
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is non-zero.
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Events
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======
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The OMAP 3 ISP driver does support the V4L2 event interface on CCDC and
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statistics (AEWB, AF and histogram) subdevs.
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The CCDC subdev produces V4L2_EVENT_OMAP3ISP_HS_VS type event on HS_VS
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interrupt which is used to signal frame start. The event is triggered exactly
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when the reception of the first line of the frame starts in the CCDC module.
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The event can be subscribed on the CCDC subdev.
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(When using parallel interface one must pay account to correct configuration
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of the VS signal polarity. This is automatically correct when using the serial
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receivers.)
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Each of the statistics subdevs is able to produce events. An event is
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generated whenever a statistics buffer can be dequeued by a user space
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application using the VIDIOC_OMAP3ISP_STAT_REQ IOCTL. The events available
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are:
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V4L2_EVENT_OMAP3ISP_AEWB
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V4L2_EVENT_OMAP3ISP_AF
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V4L2_EVENT_OMAP3ISP_HIST
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The type of the event data is struct omap3isp_stat_event_status for these
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ioctls. If there is an error calculating the statistics, there will be an
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event as usual, but no related statistics buffer. In this case
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omap3isp_stat_event_status.buf_err is set to non-zero.
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Private IOCTLs
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==============
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The OMAP 3 ISP driver supports standard V4L2 IOCTLs and controls where
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possible and practical. Much of the functions provided by the ISP, however,
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does not fall under the standard IOCTLs --- gamma tables and configuration of
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statistics collection are examples of such.
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In general, there is a private ioctl for configuring each of the blocks
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containing hardware-dependent functions.
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The following private IOCTLs are supported:
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VIDIOC_OMAP3ISP_CCDC_CFG
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VIDIOC_OMAP3ISP_PRV_CFG
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VIDIOC_OMAP3ISP_AEWB_CFG
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VIDIOC_OMAP3ISP_HIST_CFG
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VIDIOC_OMAP3ISP_AF_CFG
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VIDIOC_OMAP3ISP_STAT_REQ
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VIDIOC_OMAP3ISP_STAT_EN
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The parameter structures used by these ioctls are described in
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include/linux/omap3isp.h. The detailed functions of the ISP itself related to
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a given ISP block is described in the Technical Reference Manuals (TRMs) ---
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see the end of the document for those.
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While it is possible to use the ISP driver without any use of these private
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IOCTLs it is not possible to obtain optimal image quality this way. The AEWB,
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AF and histogram modules cannot be used without configuring them using the
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appropriate private IOCTLs.
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CCDC and preview block IOCTLs
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=============================
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The VIDIOC_OMAP3ISP_CCDC_CFG and VIDIOC_OMAP3ISP_PRV_CFG IOCTLs are used to
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configure, enable and disable functions in the CCDC and preview blocks,
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respectively. Both IOCTLs control several functions in the blocks they
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control. VIDIOC_OMAP3ISP_CCDC_CFG IOCTL accepts a pointer to struct
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omap3isp_ccdc_update_config as its argument. Similarly VIDIOC_OMAP3ISP_PRV_CFG
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accepts a pointer to struct omap3isp_prev_update_config. The definition of
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both structures is available in [1].
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The update field in the structures tells whether to update the configuration
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for the specific function and the flag tells whether to enable or disable the
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function.
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The update and flag bit masks accept the following values. Each separate
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functions in the CCDC and preview blocks is associated with a flag (either
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disable or enable; part of the flag field in the structure) and a pointer to
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configuration data for the function.
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Valid values for the update and flag fields are listed here for
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VIDIOC_OMAP3ISP_CCDC_CFG. Values may be or'ed to configure more than one
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function in the same IOCTL call.
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OMAP3ISP_CCDC_ALAW
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OMAP3ISP_CCDC_LPF
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OMAP3ISP_CCDC_BLCLAMP
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OMAP3ISP_CCDC_BCOMP
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OMAP3ISP_CCDC_FPC
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OMAP3ISP_CCDC_CULL
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OMAP3ISP_CCDC_CONFIG_LSC
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OMAP3ISP_CCDC_TBL_LSC
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The corresponding values for the VIDIOC_OMAP3ISP_PRV_CFG are here:
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OMAP3ISP_PREV_LUMAENH
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OMAP3ISP_PREV_INVALAW
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OMAP3ISP_PREV_HRZ_MED
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OMAP3ISP_PREV_CFA
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OMAP3ISP_PREV_CHROMA_SUPP
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OMAP3ISP_PREV_WB
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OMAP3ISP_PREV_BLKADJ
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OMAP3ISP_PREV_RGB2RGB
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OMAP3ISP_PREV_COLOR_CONV
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OMAP3ISP_PREV_YC_LIMIT
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OMAP3ISP_PREV_DEFECT_COR
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OMAP3ISP_PREV_GAMMABYPASS
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OMAP3ISP_PREV_DRK_FRM_CAPTURE
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OMAP3ISP_PREV_DRK_FRM_SUBTRACT
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OMAP3ISP_PREV_LENS_SHADING
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OMAP3ISP_PREV_NF
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OMAP3ISP_PREV_GAMMA
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The associated configuration pointer for the function may not be NULL when
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enabling the function. When disabling a function the configuration pointer is
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ignored.
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Statistic blocks IOCTLs
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=======================
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The statistics subdevs do offer more dynamic configuration options than the
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other subdevs. They can be enabled, disable and reconfigured when the pipeline
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is in streaming state.
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The statistics blocks always get the input image data from the CCDC (as the
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histogram memory read isn't implemented). The statistics are dequeueable by
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the user from the statistics subdev nodes using private IOCTLs.
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The private IOCTLs offered by the AEWB, AF and histogram subdevs are heavily
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reflected by the register level interface offered by the ISP hardware. There
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are aspects that are purely related to the driver implementation and these are
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discussed next.
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VIDIOC_OMAP3ISP_STAT_EN
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-----------------------
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This private IOCTL enables/disables a statistic module. If this request is
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done before streaming, it will take effect as soon as the pipeline starts to
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stream. If the pipeline is already streaming, it will take effect as soon as
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the CCDC becomes idle.
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VIDIOC_OMAP3ISP_AEWB_CFG, VIDIOC_OMAP3ISP_HIST_CFG and VIDIOC_OMAP3ISP_AF_CFG
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-----------------------------------------------------------------------------
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Those IOCTLs are used to configure the modules. They require user applications
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to have an in-depth knowledge of the hardware. Most of the fields explanation
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can be found on OMAP's TRMs. The two following fields common to all the above
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configure private IOCTLs require explanation for better understanding as they
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are not part of the TRM.
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omap3isp_[h3a_af/h3a_aewb/hist]_config.buf_size:
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The modules handle their buffers internally. The necessary buffer size for the
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module's data output depends on the requested configuration. Although the
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driver supports reconfiguration while streaming, it does not support a
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reconfiguration which requires bigger buffer size than what is already
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internally allocated if the module is enabled. It will return -EBUSY on this
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case. In order to avoid such condition, either disable/reconfigure/enable the
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module or request the necessary buffer size during the first configuration
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while the module is disabled.
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The internal buffer size allocation considers the requested configuration's
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minimum buffer size and the value set on buf_size field. If buf_size field is
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out of [minimum, maximum] buffer size range, it's clamped to fit in there.
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The driver then selects the biggest value. The corrected buf_size value is
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written back to user application.
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omap3isp_[h3a_af/h3a_aewb/hist]_config.config_counter:
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As the configuration doesn't take effect synchronously to the request, the
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driver must provide a way to track this information to provide more accurate
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data. After a configuration is requested, the config_counter returned to user
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space application will be an unique value associated to that request. When
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user application receives an event for buffer availability or when a new
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buffer is requested, this config_counter is used to match a buffer data and a
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configuration.
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VIDIOC_OMAP3ISP_STAT_REQ
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------------------------
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Send to user space the oldest data available in the internal buffer queue and
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discards such buffer afterwards. The field omap3isp_stat_data.frame_number
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matches with the video buffer's field_count.
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Technical reference manuals (TRMs) and other documentation
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==========================================================
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OMAP 3430 TRM:
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<URL:http://focus.ti.com/pdfs/wtbu/OMAP34xx_ES3.1.x_PUBLIC_TRM_vZM.zip>
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Referenced 2011-03-05.
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OMAP 35xx TRM:
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<URL:http://www.ti.com/litv/pdf/spruf98o> Referenced 2011-03-05.
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OMAP 3630 TRM:
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<URL:http://focus.ti.com/pdfs/wtbu/OMAP36xx_ES1.x_PUBLIC_TRM_vQ.zip>
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Referenced 2011-03-05.
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DM 3730 TRM:
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<URL:http://www.ti.com/litv/pdf/sprugn4h> Referenced 2011-03-06.
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References
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==========
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[1] include/linux/omap3isp.h
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[2] http://git.ideasonboard.org/?p=media-ctl.git;a=summary
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