|
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 1/1] cameraif: add ABI for para-virtual camera
Hi, Hans! Thank you for valuable comments and valid concerns! On 09/12/2018 10:52 AM, Hans Verkuil wrote: On 09/11/2018 10:29 AM, Oleksandr Andrushchenko wrote:From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> This is the ABI for the two halves of a para-virtualized camera driver which extends Xen's reach multimedia capabilities even farther enabling it for video conferencing, In-Vehicle Infotainment, high definition maps etc. The initial goal is to support most needed functionality with the final idea to make it possible to extend the protocol if need be: 1. Provide means for base virtual device configuration: - pixel formats - resolutions - frame rates 2. Support basic camera controls: - contrast - brightness - hue - saturation 3. Support streaming control 4. Support zero-copying use-cases Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> --- xen/include/public/io/cameraif.h | 1263 ++++++++++++++++++++++++++++++ 1 file changed, 1263 insertions(+) create mode 100644 xen/include/public/io/cameraif.h diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h new file mode 100644 index 000000000000..38b9b3741e75 --- /dev/null +++ b/xen/include/public/io/cameraif.h @@ -0,0 +1,1263 @@ +/****************************************************************************** + * cameraif.h + * + * Unified camera device I/O interface for Xen guest OSes. + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to + * deal in the Software without restriction, including without limitation the + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or + * sell copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER + * DEALINGS IN THE SOFTWARE. + * + * Copyright (C) 2018 EPAM Systems Inc. + * + * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> + */ + +#ifndef __XEN_PUBLIC_IO_CAMERAIF_H__ +#define __XEN_PUBLIC_IO_CAMERAIF_H__ + +#include "ring.h" +#include "../grant_table.h" + +/* + ****************************************************************************** + * Protocol version + ****************************************************************************** + */ +#define XENCAMERA_PROTOCOL_VERSION "1" + +/* + ****************************************************************************** + * Feature and Parameter Negotiation + ****************************************************************************** + * + * Front->back notifications: when enqueuing a new request, sending a + * notification can be made conditional on xencamera_req (i.e., the generic + * hold-off mechanism provided by the ring macros). Backends must set + * xencamera_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()). + * + * Back->front notifications: when enqueuing a new response, sending a + * notification can be made conditional on xencamera_resp (i.e., the generic + * hold-off mechanism provided by the ring macros). Frontends must set + * xencamera_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()). + * + * The two halves of a para-virtual camera driver utilize nodes within + * XenStore to communicate capabilities and to negotiate operating parameters. + * This section enumerates these nodes which reside in the respective front and + * backend portions of XenStore, following the XenBus convention. + * + * All data in XenStore is stored as strings. Nodes specifying numeric + * values are encoded in decimal. Integer value ranges listed below are + * expressed as fixed sized integer types capable of storing the conversion + * of a properly formatted node string, without loss of information. + * + ****************************************************************************** + * Example configuration + ****************************************************************************** + * + * This is an example of backend and frontend configuration: + * + *--------------------------------- Backend ----------------------------------- + * + * /local/domain/0/backend/vcamera/1/0/frontend-id = "1" + * /local/domain/0/backend/vcamera/1/0/frontend = "/local/domain/1/device/vcamera/0" + * /local/domain/0/backend/vcamera/1/0/state = "4" + * /local/domain/0/backend/vcamera/1/0/versions = "1,2" + * + *--------------------------------- Frontend ---------------------------------- + * + * /local/domain/1/device/vcamera/0/backend-id = "0" + * /local/domain/1/device/vcamera/0/backend = "/local/domain/0/backend/vcamera/1" + * /local/domain/1/device/vcamera/0/state = "4" + * /local/domain/1/device/vcamera/0/version = "1" + * /local/domain/1/device/vcamera/0/be-alloc = "1" + * + *---------------------------- Device 0 configuration ------------------------- + * + * /local/domain/1/device/vcamera/0/controls = "contrast,hue" + * /local/domain/1/device/vcamera/0/formats/YUYV/640x480/frame-rates = "30/1,15/1" + * /local/domain/1/device/vcamera/0/formats/YUYV/1920x1080/frame-rates = "15/2" + * /local/domain/1/device/vcamera/0/formats/BGRA/640x480/frame-rates = "15/1,15/2" + * /local/domain/1/device/vcamera/0/formats/BGRA/1200x720/frame-rates = "15/2" + * /local/domain/1/device/vcamera/0/unique-id = "0" + * /local/domain/1/device/vcamera/0/req-ring-ref = "2832" + * /local/domain/1/device/vcamera/0/req-event-channel = "15" + * /local/domain/1/device/vcamera/0/evt-ring-ref = "387" + * /local/domain/1/device/vcamera/0/evt-event-channel = "16" + * + *---------------------------- Device 1 configuration ------------------------- + * + * /local/domain/1/device/vcamera/1/controls = "brightness,saturation,hue" + * /local/domain/1/device/vcamera/1/formats/YUYV/640x480/frame-rates = "30/1,15/2" + * /local/domain/1/device/vcamera/1/formats/YUYV/1920x1080/frame-rates = "15/2" + * /local/domain/1/device/vcamera/1/unique-id = "1" + * /local/domain/1/device/vcamera/1/req-ring-ref = "2833" + * /local/domain/1/device/vcamera/1/req-event-channel = "17" + * /local/domain/1/device/vcamera/1/evt-ring-ref = "388" + * /local/domain/1/device/vcamera/1/evt-event-channel = "18" + * + ****************************************************************************** + * Backend XenBus Nodes + ****************************************************************************** + * + *----------------------------- Protocol version ------------------------------ + * + * versions + * Values: <string> + * + * List of XENCAMERA_LIST_SEPARATOR separated protocol versions supported + * by the backend. For example "1,2,3". + * + ****************************************************************************** + * Frontend XenBus Nodes + ****************************************************************************** + * + *-------------------------------- Addressing --------------------------------- + * + * dom-id + * Values: <uint16_t> + * + * Domain identifier. + * + * dev-id + * Values: <uint16_t> + * + * Device identifier. + * + * /local/domain/<dom-id>/device/vcamera/<dev-id>/... + * + *----------------------------- Protocol version ------------------------------ + * + * version + * Values: <string> + * + * Protocol version, chosen among the ones supported by the backend. + * + *------------------------- Backend buffer allocation ------------------------- + * + * be-alloc + * Values: "0", "1" + * + * If value is set to "1", then backend will be the buffer + * provider/allocator for this domain during XENCAMERA_OP_BUF_CREATE + * operation. + * If value is not "1" or omitted frontend must allocate buffers itself. + * + *------------------------------- Camera settings ----------------------------- + * + * unique-id + * Values: <string> + * + * After device instance initialization each camera is assigned a + * unique ID, so it can be identified by the backend by this ID. + * This can be UUID or such. + * + * controls + * Values: <list of string> + * + * List of supported camera controls separated by XENCAMERA_LIST_SEPARATOR. + * Camera controls are expressed as a list of string values w/o any + * ordering requirement. + * + * formats + * Values: <format, char[4]> + * + * Formats are organized as a set of directories one per each + * supported pixel format. The name of the directory is the + * corresponding FOURCC string label. The next level of + * the directory under <formats> represents supported resolutions.So how will this work for a pixelformat like V4L2_PIX_FMT_ARGB555X? As mentioned before, we display such formats as 'XXXX-BE', i.e. char[7]. ok, then I'll change this to char[7] and put a note on big-endian: * If format represents a big-endian FOURCC code, then "-BE" * suffix must be added, case insensitive. I assume the pixelformats you use here are based on the V4L2_PIX_FMT_ fourccs? Note that there is no real standard for fourcc values, so if you want to support a Windows backend as well, then you'll need mappings from whatever Windows uses to the V4L2 fourccs. The V4L2_PIX_FMT_ fourccs are entirely V4L2 specific. So you have to define here whose fourccs you are using. I thought that [1] defines all these values, but if this is not the case, then I think we can use what V4L2 uses. In this case, what would be the best reference in the protocol to those fourcc codes? For example, I can reference [2] in the protocol's assumptions: ****************************************************************************** * Assumptions ****************************************************************************** ... * - all FOURCC mappings used for configuration and messaging are* Linux V4L2 ones: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/videodev2.h + * + * resolution + * Values: <width, uint32_t>x<height, uint32_t> + * + * Resolutions are organized as a set of directories one per each + * supported resolution under corresponding <formats> directory. + * The name of the directory is the supported width and height + * of the camera resolution in pixels.So how will this work for sources like HDMI where the resolution depends on the signal? Will this only show the received resolution? And if so, what happens if there is no signal? Or the resolution changes? If you want to support such devices, you'll need to define the behavior. It might be OK to rely on the XenbusStateReconfiguring state, but I think this would have to be described somewhere. I.e. if the source is disconnected, then you enter state XenbusStateReconfiguring, when a new source is connected, then you setup a new configuration based on the newly detected timings. But what to do when the timings change? Reconfiguring again? Whether this is an option depends in part on how long it takes before the new configuration becomes active. Well, IMO this is something which is a part of the backend's logic: backend may decide to tear down the whole virtual camera device, e.g. going into closed state, or it can try reconfiguring the device or whatever. One note on such complex use-cases: we are trying to keep the protocol as simple as possible not trying to mimic really complex HW. If need be to support this one can probably just pass through that HW device to a guest, so it can benefit from all those features. Most use-cases we see only need captured frames and most of the work of getting those is handled by the backend. And the configuration most of the time should remain static, e.g. all the parameters are defined for known HW and VMs are configured with specific use-cases in mind. Thus, the backend should hide all the real complexity from a virtual camera device driver as much as it can (BTW, frontend might not be a V4L2 device driver, but a unikernel application for instance) + * + * frame-rates + * Values: <numerator, uint32_t>/<denominator, uint32_t> + * + * List of XENCAMERA_FRAME_RATE_SEPARATOR separated supported frame rates + * of the camera expressed as numerator and denominator of the + * corresponding frame rate.Note that there are devices that allow a range of resolutions and framerates instead of a discrete set of resolutions/framerates. Whether or not that is something you want to care about here is another matter. A device that has a range of resolutions typically has a scaler on board. A range of framerates typically means that it has fine-grained control over the sensor pixelclock and whatever else is related to the framerate. Yes, that was intentionally that we only support discrete values, please see above - most of the time you don't need a fully blown virtual camera + * + *------------------- Camera Request Transport Parameters --------------------- + * + * This communication path is used to deliver requests from frontend to backend + * and get the corresponding responses from backend to frontend, + * set up per virtual camera device. + * + * req-event-channel + * Values: <uint32_t> + * + * The identifier of the Xen camera's control event channel + * used to signal activity in the ring buffer. + * + * req-ring-ref + * Values: <uint32_t> + * + * The Xen grant reference granting permission for the backend to map + * a sole page of camera's control ring buffer. + * + *-------------------- Camera Event Transport Parameters ---------------------- + * + * This communication path is used to deliver asynchronous events from backend + * to frontend, set up per virtual camera device. + * + * evt-event-channel + * Values: <uint32_t> + * + * The identifier of the Xen camera's event channel + * used to signal activity in the ring buffer. + * + * evt-ring-ref + * Values: <uint32_t> + * + * The Xen grant reference granting permission for the backend to map + * a sole page of camera's event ring buffer. + */ + +/* + ****************************************************************************** + * STATE DIAGRAMS + ****************************************************************************** + * + * Tool stack creates front and back state nodes with initial state + * XenbusStateInitialising. + * Tool stack creates and sets up frontend camera configuration + * nodes per domain. + * + *-------------------------------- Normal flow -------------------------------- + * + * Front Back + * ================================= ===================================== + * XenbusStateInitialising XenbusStateInitialising + * o Query backend device identification + * data. + * o Open and validate backend device. + * | + * | + * V + * XenbusStateInitWait + * + * o Query frontend configuration + * o Allocate and initialize + * event channels per configured + * camera. + * o Publish transport parameters + * that will be in effect during + * this connection. + * | + * | + * V + * XenbusStateInitialised + * + * o Query frontend transport parameters. + * o Connect to the event channels. + * | + * | + * V + * XenbusStateConnected + * + * o Create and initialize OS + * virtual camera as per + * configuration. + * | + * | + * V + * XenbusStateConnected + * + * XenbusStateUnknown + * XenbusStateClosed + * XenbusStateClosing + * o Remove virtual camera device + * o Remove event channels + * | + * | + * V + * XenbusStateClosed + * + *------------------------------- Recovery flow ------------------------------- + * + * In case of frontend unrecoverable errors backend handles that as + * if frontend goes into the XenbusStateClosed state. + * + * In case of backend unrecoverable errors frontend tries removing + * the virtualized device. If this is possible at the moment of error, + * then frontend goes into the XenbusStateInitialising state and is ready for + * new connection with backend. If the virtualized device is still in use and + * cannot be removed, then frontend goes into the XenbusStateReconfiguring state + * until either the virtualized device is removed or backend initiates a new + * connection. On the virtualized device removal frontend goes into the + * XenbusStateInitialising state. + * + * Note on XenbusStateReconfiguring state of the frontend: if backend has + * unrecoverable errors then frontend cannot send requests to the backend + * and thus cannot provide functionality of the virtualized device anymore. + * After backend is back to normal the virtualized device may still hold some + * state: configuration in use, allocated buffers, client application state etc. + * In most cases, this will require frontend to implement complex recovery + * reconnect logic. Instead, by going into XenbusStateReconfiguring state, + * frontend will make sure no new clients of the virtualized device are + * accepted, allow existing client(s) to exit gracefully by signaling error + * state etc. + * Once all the clients are gone frontend can reinitialize the virtualized + * device and get into XenbusStateInitialising state again signaling the + * backend that a new connection can be made. + * + * There are multiple conditions possible under which frontend will go from + * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS + * specific. For example: + * 1. The underlying OS framework may provide callbacks to signal that the last + * client of the virtualized device has gone and the device can be removed + * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue) + * to periodically check if this is the right time to re-try removal of + * the virtualized device. + * 3. By any other means. + * + ****************************************************************************** + * REQUEST CODES + ****************************************************************************** + */ +#define XENCAMERA_OP_CONFIG_SET 0x00 +#define XENCAMERA_OP_CONFIG_GET 0x01 +#define XENCAMERA_OP_BUF_REQUEST 0x02 +#define XENCAMERA_OP_BUF_CREATE 0x03 +#define XENCAMERA_OP_BUF_DESTROY 0x04 +#define XENCAMERA_OP_BUF_QUEUE 0x05 +#define XENCAMERA_OP_BUF_DEQUEUE 0x06 +#define XENCAMERA_OP_CTRL_ENUM 0x07 +#define XENCAMERA_OP_CTRL_SET 0x08 +#define XENCAMERA_OP_CTRL_GET 0x09 +#define XENCAMERA_OP_STREAM_START 0x0a +#define XENCAMERA_OP_STREAM_STOP 0x0b + +#define XENCAMERA_CTRL_BRIGHTNESS 0 +#define XENCAMERA_CTRL_CONTRAST 1 +#define XENCAMERA_CTRL_SATURATION 2 +#define XENCAMERA_CTRL_HUE 3 + +/* Number of supported controls. */ +#define XENCAMERA_MAX_CTRL 4 + +/* Control is read-only. */ +#define XENCAMERA_CTRL_FLG_RO (1 << 0) +/* Control is write-only. */ +#define XENCAMERA_CTRL_FLG_WO (1 << 1) +/* Control's value is volatile. */ +#define XENCAMERA_CTRL_FLG_VOLATILE (1 << 2) + +/* Supported color spaces. */ +#define XENCAMERA_COLORSPACE_SMPTE170M 0 +#define XENCAMERA_COLORSPACE_REC709 1 +#define XENCAMERA_COLORSPACE_SRGB 2 +#define XENCAMERA_COLORSPACE_ADOBERGB 3Right, this is something I haven't done yet: replace ADOBERGB with OPRGB. Will do here and below, thank you for clarifying Adobe doesn't like others using its name for the colorspace, and in fact all references in the CTA-861-G standard to Adobe have been replaced with opRGB, which is the name of the official standard. opRGB is really identical to AdobeRGB, but if you are going to make new defines you might just as well use the official name. I still need to make patches for the kernel to do a similar substitution.+#define XENCAMERA_COLORSPACE_BT2020 4 +#define XENCAMERA_COLORSPACE_DCI_P3 5 +#define XENCAMERA_COLORSPACE_RAW 6 + +/* Color space transfer function. */ +#define XENCAMERA_XFER_FUNC_709 0 +#define XENCAMERA_XFER_FUNC_SRGB 1 +#define XENCAMERA_XFER_FUNC_ADOBERGB 2Ditto.+#define XENCAMERA_XFER_FUNC_NONE 3 +#define XENCAMERA_XFER_FUNC_DCI_P3 4 +#define XENCAMERA_XFER_FUNC_SMPTE2084 5 + +/* Color space Y’CbCr encoding. */ +#define XENCAMERA_YCBCR_ENC_601 0 +#define XENCAMERA_YCBCR_ENC_709 1 +#define XENCAMERA_YCBCR_ENC_XV601 2 +#define XENCAMERA_YCBCR_ENC_XV709 3 +#define XENCAMERA_YCBCR_ENC_BT2020 4 +#define XENCAMERA_YCBCR_ENC_BT2020_CONST_LUM 5 + +/* Quantization range. */ +#define XENCAMERA_QUANTIZATION_FULL_RANGE 0 +#define XENCAMERA_QUANTIZATION_LIM_RANGE 1 + +/* + ****************************************************************************** + * EVENT CODES + ****************************************************************************** + */ +#define XENCAMERA_EVT_FRAME_AVAIL 0x00 +#define XENCAMERA_EVT_CONFIG_CHANGE 0x01 +#define XENCAMERA_EVT_CTRL_CHANGE 0x02 + +/* Resolution has changed. */ +#define XENCAMERA_EVT_CFG_FLG_RESOL (1 << 0) + +/* + ****************************************************************************** + * XENSTORE FIELD AND PATH NAME STRINGS, HELPERS + ****************************************************************************** + */ +#define XENCAMERA_DRIVER_NAME "vcamera" + +#define XENCAMERA_LIST_SEPARATOR "," +#define XENCAMERA_RESOLUTION_SEPARATOR "x" +#define XENCAMERA_FRACTION_SEPARATOR "/" + +#define XENCAMERA_FIELD_BE_VERSIONS "versions" +#define XENCAMERA_FIELD_FE_VERSION "version" +#define XENCAMERA_FIELD_REQ_RING_REF "req-ring-ref" +#define XENCAMERA_FIELD_REQ_CHANNEL "req-event-channel" +#define XENCAMERA_FIELD_EVT_RING_REF "evt-ring-ref" +#define XENCAMERA_FIELD_EVT_CHANNEL "evt-event-channel" +#define XENCAMERA_FIELD_CONTROLS "controls" +#define XENCAMERA_FIELD_FORMATS "formats" +#define XENCAMERA_FIELD_FRAME_RATES "frame-rates" +#define XENCAMERA_FIELD_BE_ALLOC "be-alloc" +#define XENCAMERA_FIELD_UNIQUE_ID "unique-id" + +#define XENCAMERA_CTRL_BRIGHTNESS_STR "brightness" +#define XENCAMERA_CTRL_CONTRAST_STR "contrast" +#define XENCAMERA_CTRL_SATURATION_STR "saturation" +#define XENCAMERA_CTRL_HUE_STR "hue" + +/* Maximum number of buffer planes supported. */ +#define XENCAMERA_MAX_PLANE 4 + +/* + ****************************************************************************** + * STATUS RETURN CODES + ****************************************************************************** + * + * Status return code is zero on success and -XEN_EXX on failure. + * + ****************************************************************************** + * Assumptions + ****************************************************************************** + * + * - usage of grant reference 0 as invalid grant reference: + * grant reference 0 is valid, but never exposed to a PV driver, + * because of the fact it is already in use/reserved by the PV console. + * - all references in this document to page sizes must be treated + * as pages of size XEN_PAGE_SIZE unless otherwise noted. + * + ****************************************************************************** + * Description of the protocol between frontend and backend driver + ****************************************************************************** + * + * The two halves of a Para-virtual camera driver communicate with + * each other using shared pages and event channels. + * Shared page contains a ring with request/response packets. + * + * All reserved fields in the structures below must be 0. + * + * For all request/response/event packets: + * - frame rate parameter is represented as a pair of 4 octet long + * numerator and denominator: + * - frame_rate_numer - uint32_t, numerator of the frame rate + * - frame_rate_denom - uint32_t, denominator of the frame rate + * The corresponding frame rate (Hz) is calculated as: + * frame_rate = frame_rate_numer / frame_rate_denom + * - buffer index is a zero based index of the buffer. Must be less than + * the value of XENCAMERA_OP_CONFIG_SET.num_bufs response: + * - index - uint8_t, index of the buffer. + * + * + *---------------------------------- Requests --------------------------------- + * + * All request packets have the same length (64 octets). + * All request packets have common header: + * 0 1 2 3 octet + * +----------------+----------------+----------------+----------------+ + * | id | operation | reserved | 4 + * +----------------+----------------+----------------+----------------+ + * | reserved | 8 + * +----------------+----------------+----------------+----------------+ + * id - uint16_t, private guest value, echoed in response. + * operation - uint8_t, operation code, XENCAMERA_OP_XXX. + * + * + * Request to set configuration - request to set the configuration/mode + * of the camera: + * 0 1 2 3 octet + * +----------------+----------------+----------------+----------------+ + * | id | _OP_CONFIG_SET | reserved | 4 + * +----------------+----------------+----------------+----------------+ + * | reserved | 8 + * +----------------+----------------+----------------+----------------+ + * | pixel format | 12 + * +----------------+----------------+----------------+----------------+ + * | width | 16 + * +----------------+----------------+----------------+----------------+ + * | height | 20 + * +----------------+----------------+----------------+----------------+ + * | colorspace | 24 + * +----------------+----------------+----------------+----------------+ + * | xfer_func | 28 + * +----------------+----------------+----------------+----------------+ + * | ycbcr_enc | 32 + * +----------------+----------------+----------------+----------------+ + * | quantization | 36 + * +----------------+----------------+----------------+----------------+ + * | displ_asp_ratio_numer | 40 + * +----------------+----------------+----------------+----------------+ + * | displ_asp_ratio_denom | 44 + * +----------------+----------------+----------------+----------------+ + * | frame_rate_numer | 48 + * +----------------+----------------+----------------+----------------+ + * | frame_rate_denom | 52 + * +----------------+----------------+----------------+----------------+ + * | reserved | 56 + * +----------------+----------------+----------------+----------------+ + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/| + * +----------------+----------------+----------------+----------------+ + * | reserved | 64 + * +----------------+----------------+----------------+----------------+ + * + * pixel_format - uint32_t, pixel format to be used, FOURCC code. + * width - uint32_t, width in pixels. + * height - uint32_t, height in pixels. + * colorspace - uint32_t, this supplements pixel_format parameter, + * one of the XENCAMERA_COLORSPACE_XXX. + * xfer_func - uint32_t, this supplements colorspace parameter, + * one of the XENCAMERA_XFER_FUNC_XXX. + * ycbcr_enc - uint32_t, this supplements colorspace parameter, + * one of the XENCAMERA_YCBCR_ENC_XXX.You do need to mention that ycbcr_enc is only valid for YCbCr pixelformats and that it should be ignore otherwise. Or perhaps add a define just for that: #define XENCAMERA_YCBCR_ENC_IGNORE 0 I will both define and put a note: * ycbcr_enc - uint32_t, this supplements colorspace parameter,* one of the XENCAMERA_YCBCR_ENC_XXX. Please note, that ycbcr_enc is only * valid for YCbCr pixelformats and should be ignored otherwise.
As this request's response has buffer layout, I was planning to use num_bufs == 0 as a way to request that layout w/o allocating the buffers: * - passing zero num_bufs in this request is not an error and is used * to query buffer's format So BUF_REQUEST maps to VIDIOC_REQBUFS and once called it fixes the format in place, i.e. after this you can no longer change the format. I'll put a note on this, thank you: * - after this request camera configuration cannot be changed, unless * streaming is stopped and buffers destroyed Changing the format usually means changing the buffer size, but once they are allocated with REQBUFS that is no longer possible. If you want to change the format, then the first thing you have to do is stop streaming and releasing all buffers. This last step is done with VIDIOC_REQBUFS with a count of 0. This will be the frontend's responsibility to do so: 1. stop streaming 2. destroy buffers In case of a V4L2 frontend this will be while serving "VIDIOC_REQBUFS with a count of 0". Whether or not you want to do the same thing (i.e. if num_bufs == 0, then free all buffers) is up to you, but you do need a similar mechanism in your API. And you need to document that once buffers are allocated, you can't change the configuration anymore. Please see the note above
Will change to uint32_t +}; + +/* + * Control enumerate response - response for XENCAMERA_OP_CTRL_ENUM: + * 0 1 2 3 octet + * +----------------+----------------+----------------+----------------+ + * | id | _OP_CTRL_ENUM | reserved | 4 + * +----------------+----------------+----------------+----------------+ + * | status | 8 + * +----------------+----------------+----------------+----------------+ + * | index | type | flags | 12 + * +----------------+----------------+----------------+----------------+ + * | reserved | 16 + * +----------------+----------------+----------------+----------------+ + * | min low 32-bits | 20 + * +----------------+----------------+----------------+----------------+ + * | min high 32-bits | 24 + * +----------------+----------------+----------------+----------------+ + * | max low 32-bits | 28 + * +----------------+----------------+----------------+----------------+ + * | max high 32-bits | 32 + * +----------------+----------------+----------------+----------------+ + * | step low 32-bits | 36 + * +----------------+----------------+----------------+----------------+ + * | step high 32-bits | 40 + * +----------------+----------------+----------------+----------------+ + * | def_val low 32-bits | 44 + * +----------------+----------------+----------------+----------------+ + * | def_val high 32-bits | 48 + * +----------------+----------------+----------------+----------------+ + * | reserved | 52 + * +----------------+----------------+----------------+----------------+ + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/| + * +----------------+----------------+----------------+----------------+ + * | reserved | 64 + * +----------------+----------------+----------------+----------------+ + * + * index - uint8_t, index of the camera control in response. + * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX. + * flags - uint16_t, flags of the control, one of the XENCAMERA_CTRL_FLG_XXX.Go with a uint32_t for the flags. V4L2 is already using 11 flags... ok, will change to uint32_t
I'll put a note on this: * seq_num - uint64_t, sequential number of the frame. Must be * monotonically increasing. If skips are detected in seq_num then that * means that the frames in-between were dropped.
That effectively means almost the same as going into Closed state and then going back into Connected state which can be controlled by the backend with XenBus state machine. So, this particular configuration change event can be omitted at all. Does this sound reasonable? But what if there is no new config because the source was disconnected? This is the backend's responsibility to control that, e.g. if the source has disconnected then the backend must hold virtual camera device via the XenBus state machine in closed or any non-operatable state until that source comes back. + +/* + * Control change event- event from back to front when camera control + * has changed: + * 0 1 2 3 octet + * +----------------+----------------+----------------+----------------+ + * | id |_EVT_CTRL_CHANGE| reserved | 4 + * +----------------+----------------+----------------+----------------+ + * | type | reserved | 8 + * +----------------+----------------+----------------+----------------+ + * | reserved | 12 + * +----------------+----------------+----------------+----------------+ + * | reserved | 16 + * +----------------+----------------+----------------+----------------+ + * | value low 32-bit | 20 + * +----------------+----------------+----------------+----------------+ + * | value high 32-bit | 24 + * +----------------+----------------+----------------+----------------+ + * | reserved | 28 + * +----------------+----------------+----------------+----------------+ + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/| + * +----------------+----------------+----------------+----------------+ + * | reserved | 64 + * +----------------+----------------+----------------+----------------+ + * + * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX. + * value - int64_t, new value of the control. + */So will this happen for all controls (except write-only)? What about volatile controls? What if the frontend sets a control, does it also get this event? Does it get this event with the current value of a control when it first connects? What happens if there are multiple quick changes to the same control? Can the event queue overflow? Sorry, these are all questions we had to answer when we added control event support. We spend a lot of time making the event handling reliable without losing information (intermediate values can be lost, but never the current value). Since this is relying on a Xen event mechanism you will have to think about this as well. I'll put these notes: * Notes: * - this event is not sent for write-only controls * - this event is also sent to the originator of the control change * - this event is not sent when frontend first connects, e.g. initial * control state must be explicitly queried
Thank you, Oleksandr [1] https://www.fourcc.org/[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/videodev2.h _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
|
 |
Lists.xenproject.org is hosted with RackSpace, monitoring our |