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.
(or alternatively, if you disagree and think CxD should be specified by s_fmt(), then how does the user specify ExF?)
Regards, Sylwester -- 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
