Hi Thomas and Sylwester, Apologies for my late reply. On Sat, Jul 06, 2013 at 09:58:23PM +0200, Sylwester Nawrocki wrote: > Hi Thomas, > > Cc: Sakari and Laurent > > On 07/05/2013 10:22 AM, Thomas Vajzovic wrote: > >Hello, > > > >I am writing a driver for the sensor MT9D131. This device supports > >digital zoom and JPEG compression. > > > >Although I am writing it for my company's internal purposes, it will > >be made open-source, so I would like to keep the API as portable as > >possible. > > > >The hardware reads AxB sensor pixels from its array, resamples them > >to CxD image pixels, and then compresses them to ExF bytes. > > > >The subdevice driver sets size AxB to the value it receives from > >v4l2_subdev_video_ops.s_crop(). > > > >To enable compression then v4l2_subdev_video_ops.s_mbus_fmt() is > >called with fmt->code=V4L2_MBUS_FMT_JPEG_1X8. > > > >fmt->width and fmt->height then ought to specify the size of the > >compressed image ExF, that is, the size specified is the size in the > >format specified (the number of JPEG_1X8), not the size it would be > >in a raw format. > > In VIDIOC_S_FMT 'sizeimage' specifies size of the buffer for the > compressed frame at the bridge driver side. And width/height should > specify size of the re-sampled (binning, skipping ?) frame - CxD, > if I understand what you are saying correctly. > > I don't quite what transformation is done at CxD -> ExF. Why you are > using ExF (two numbers) to specify number of bytes ? And how can you > know exactly beforehand what is the frame size after compression ? > Does the sensor transmit fixed number of bytes per frame, by adding > some padding bytes if required to the compressed frame data ? > > Is it something like: > > sensor matrix (AxB pixels) -> binning/skipping (CxD pixels) -> > -> JPEG compresion (width = C, height = D, sizeimage ExF bytes) > > ? > >This allows the bridge driver to be compression agnostic. It gets > >told how many bytes to allocate per buffer and it reads that many > >bytes. It doesn't have to understand that the number of bytes isn't > >directly related to the number of pixels. > > > >So how does the user tell the driver what size image to capture > >before compression, CxD? > > I think you should use VIDIOC_S_FMT(width = C, height = D, sizeimage = ExF) > for that. And s_frame_desc sudev op could be used to pass sizeimage to the > sensor subdev driver. Agreed. Let me take this into account in the next RFC. > >(or alternatively, if you disagree and think CxD should be specified > >by s_fmt(), then how does the user specify ExF?) Does the user need to specify ExF, for other purposes than limiting the size of the image? I would leave this up to the sensor driver (with reasonable alignment). The sensor driver would tell about this to the receiver through frame descriptors. (But still I don't think frame descriptors should be settable; what sensors can support is fully sensor specific and the parameters that typically need to be changed are quite limited in numbers. So I'd go with e.g. controls, again.) -- Sakari Ailus e-mail: sakari.ailus@xxxxxx XMPP: sailus@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
