Hi Sachin,

I think when we speak of OMX, we are referring to the OMX-IL layer. This layer is supported as middleware component.

I am putting down my experiences as below:
- Generally Camera gives two streams. One is preview which can be YUV/RGB and another is capture (YUV/RGB/JPEG). Preview
 frame format must be in one of display systems supported(YUV/RGB) format. Else color conversion is required in the path.
 This adds overhead and latency.

- If we have a camera sensor which is smart, i.e., it is capable of providing the processed image(RGB, YUV) frame rather
 than RAW pixel dump, and ARM is able to control the sensor interface, then V4L2 framework camera driver would work.
 User space wrapper/app would be invoking the V4L2 ioctl's to control the camera.

- If we have a RAW sensor which produces, say Bayer pixel format, we will have to have an image pipe to process it before
 converting this to one of RGB/YUV formats. Image pipes involves conversions, resizing etc. It would be an overhead
 to do these stages in ARM, and some vendors have proprietary imaging processors for it. These processors may run a custom RTOS.

 They may have built a private IPC layer into linux kernel and proprietary OS. OMX layer works in such scenarios.
 A concept called distributed OMX works on RPC mechanism. OMX client calls will now land up on the image processor from ARM.
 Again some proprietary driver/s will be invoked from the remote OMX component which would do the image processing mentioned above.

 User space wrapper/app aka OMX client, is a set of OMX calls, which will get routed to proper OMX component through OMX core. This
 is similar to V4L2 client, but instead of controlling camera through IOCTL's, we use OMX specific functions Get/Set methods.

From my view, the choice of choosing V4L2 or OMX is basically depending on the type of sensors and presence of dedicated hardware.
If we already have a dedicated imaging processor, V4L2 can be absent, and we will have to leverage the OMX because of its capability.
But if we are integrating a new sensor which has in-built accelerator, it makes sense to reduce the silicon area on SoC and use V4L2 instead.

Regards,
Subash

-------Original Message--------
 Sent: Sachin Gupta <sachin.gupta@linaro.org>
 Date: Tue, 8 Feb 2011 14:25:21 +0530
 Subject: Re: v4l2 vs omx for camera



Arnd,

  you are correct that omx and v4l2 sit at different levels one being userside API and other being kernel API.But from the point of view of integrating these API's in OS frameworks like gstreamer,Android camera service they are at the same level.I mean one will have to implement gstreamer source plugin based on either v4l2 or Omx.Also the way vendors(STE and TI) have gone about implementing OMX, they completely bypass v4l2 .The major reason being code sharing among different OS environments.The kernel side for OMX implementation just facilitates RPC between imaging coprocessor and ARM side..

Sachin


On Tue, Feb 8, 2011 at 2:00 PM, Lee Jones <lee.jones@linaro.org> wrote:

Bringing in my boys.

Robert, Linus, what say you?


On 07/02/11 12:33, Arnd Bergmann wrote:
> On Monday 07 February 2011, Sachin Gupta wrote:
>>     In Multimedia WG we have been posed with a question regarding best way
>> to expose low level API for camera.so this a questions mainly about pros and
>> cons of v4l2 and omx over each other.So to involve a wider community to
>> discuss this topic I am floating this mail on linaro-dev.Please share your
>> view/experiences.Also please involve any body else in this mail who can
>> provide valuable inputs on this.
> I've had to look up with "omx" actually stands for [1][2], but from
> an outsider view, they don't seem to be mutually exclusive or even
> competing interfaces. v4l2 is the interface you use to get at camera
> data, in whatever format the camera gives you. There are no alternatives
> to that. OpenMax gives you a way to accelerate video codecs, which
> is good, but this sits a layer higher up in the stack. Supporting omx
> is probably a good idea, but would be totally optional.
>
>       Arnd
>
> [1] http://www.khronos.org/openmax/
> [2] http://www.freedesktop.org/wiki/GstOpenMAX
>

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-------Original Message--------
 Sent: Loïc Minier <loic.minier@linaro.org>
 Date: Tue, 8 Feb 2011 10:35:38 +0100
 Subject: Re: Efikamx bootloader help

hey adding my bits where I can On Tue, Feb 08, 2011, Eric Miao wrote: > 2. The three possible boot up methods: a) Internal SPI NOR flash, b) the > MicroSD card behind the battery and c) the normal SD card at the left > side, not really sure about the situation on Efika MX (smart top) as > I don't have one in my hands efikamx only has SD and internal flash; there might be other boot methods like serial or USB, but I don't think we need to care too much about these > 4. The boot sequence of the Internal SPI NOR flash, as it looks to me that > it's trying to find boot.scr from either the MicroSD or SD card on the > first partition? Also it would be helpful to document the envionment > variables of this specific u-boot. on my efikamx, this is the bootcmd it had when I received it and corresponding variables: bootcmd=run pata_boot pata_boot=run bootargs_base bootargs_pata bootargs_base=setenv bootargs noinitrd console=ttymxc0,115200 console=tty1 bootargs_pata=setenv bootargs ${bootargs} root=/dev/sda2 ${bootinfo};run boot_pata bootinfo=rw boot_pata=run base_cmds;ide reset;fatload ide 0:1 ${loadaddr} ${kernel}; bootm ${loadaddr} base_cmds=run base_cmd1;run base_cmd2;run base_cmd3;run base_cmd4;run base_cmd5;run base_cmd99 loadaddr=0x90007FC0 kernel=uImage base_cmd1=pmic 15 0x00400022;mw.l 0x73fa84b8 0xe7 1;mw.l 0x73fd4014 0x59239100 1 base_cmd2=mw.l 0x83fd9010 0xcaaaf6d0 1;mw.l 0x73f88000 0x01025200 1;mw.l 0x73f84000 0x20 1 base_cmd3=mw.l 0x83fd9004 0x333574aa 1;mw.l 0x83fd900c 0x333574aa 1; base_cmd4=mw.l 0x83fd9020 0x00f48b00 1;mw.l 0x83fd9024 0x00f49700 1;mw.l 0x83fd9028 0x00f48700 1 base_cmd5=mw.l 0x83fd902c 0x00f48400 1;mw.l 0x83fd9030 0x00f44e00 1; > 5. If Linaro is going to support u-boot for Efika MX/SB, it's better to > follow what is in upstream. However, there could be some differences > between the u-boot in the recovery/installing image downloadable from > powerdeveloper.org and the one in upstream. We might need to figure > out those differences and see how to handle them. That was indeed the case; Marex, who developed the upstream u-boot bits, told me the same u-boot would work on SD and on flash; the one I've built from mainline uses the default imximage.cfg settings which is "BOOT_FROM spi", yet works fine from a SD card. So it seems the same u-boot can be used for both SD and flash -- just with different bootcmd. Cheers, -- Loïc Minier
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