Hi Guennadi, Thanks for the response, it's good just to get confirmation that I was indeed interpreting the code properly.
I guess the main reason this is more significant for me is the constraints I have on the hardware, i.e. it cannot handle the 640x480 at any reasonable frame rate so we need the camera hardware to provide the smaller image and second closing the camera powers the module down to conserve power, which means time from open to image capture is slow (particularly because I have to drop the first few frames with the auto white balance etc... settles). I had already assumed that streaming would need to be stopped before the size could be changed, really don't see a problem with that. I had used that approach with non-SOC style modules. I think the documentation in videobuf talks about requesting the MAX buffer size you will require from the start. So again I had already assumed I'd need to do that as well. I'm not sure I fully understand the concern about multiple simultaneous users. I certainly don't have that as a user case in my own requirements (device is a small handheld teaching aid) and I would have thought that if 2 users try to use the same camera module at the same time all hell would probably break out anyway. Have to admit I've never tried it before. Adam -----Original Message----- From: Guennadi Liakhovetski [mailto:g.liakhovet...@gmx.de] Sent: 28 October 2010 20:01 To: Adam Sutton Cc: linux-media@vger.kernel.org Subject: Re: Changing frame size on the fly in SOC module Hi Adam On Thu, 28 Oct 2010, Adam Sutton wrote: > Hi, > > Sometime ago I developed an SOC based camera driver for my platform > (ov7675 on iMX25), for the most part it seems to be working well however > at the time I couldn't manage to change the frame size on the fly > (without closing / re-opening the device). > > The current problem I have is that my application needs to display a > 320x240 preview image on screen, but to capture a static image at > 640x480. I can do this as long as I close the device in between, > unfortunately for power consumption reasons the camera device is put > into a low power state whenever the device is released. This means that > the image capture takes approx 1.5s (the requirement I have to meet is > 1s). > > Now I could cheat and simply subsample (in software) the 640x480 image, > but that puts additional burden on an already overworked MCU. > > Having been through the soc_camera and videobuf code and as far as I can > tell this inability to change the frame size without closing the camera > device appears to be a design decision. Yes, it is. > What I'm really after is confirmation one way of the other. If it's not, > what is the correct process to achieve the frame change without closing > the device. And if it is, does anybody have any suggestions of possible > workarounds? It has been decided that way, because we didn't have a good use-case for changing the frame format on-the-fly to develop for and to test with. You seem to have one now, so, go ahead;) There are a couple of issues to address though - videobuffer configuration is one of them, host reconfiguration is the other one, possible multiple simultaneous users is the third one (ok, only one of them will be actually streaming). This use case - different size preview and single shot capture has come up a couple of times before, but noone has brought it to a proper mainstream solution. One thing you'd still want to do, I think, is to stop streaming before reconfiguring, and restart it afterwards. So, maybe a viable solution would be: in soc_camera_s_fmt_vid_cap() check not just for "icf->vb_vidq.bufs[0] != NULL", but rather for if streaming is not running, and then someone will certainly have to check for large enough buffers. So, you'd have to request max size buffers from the beginning even for preview. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ Plextek Limited Registered Address: London Road, Great Chesterford, Essex, CB10 1NY, UK Company Registration No. 2305889 VAT Registration No. GB 918 4425 15 Tel: +44 1799 533 200. Fax: +44 1799 533 201 Web:http://www.plextek.com Electronics Design and Consultancy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
