Hello, On Friday, April 08, 2011 2:53 PM Laurent Pinchart wrote: > > ... > > > > > As buf_queue callback is called by vb2 only after start_streaming, > > > for a camera snapshot capture I needed to start a pipeline only from > the > > > buf_queue handler level, i.e. subdev's video s_stream op was called > from > > > within buf_queue. s_stream couldn't be done in the start_streaming > > > handler as at the time it is invoked there is always no buffer > available > > > in the bridge H/W. > > > It's a consequence of how the vb2_streamon() is designed. > > > > > > Before, I used to simply call s_stream in start_streaming, only > deferring > > > the actual bridge DMA enable till a buf_queue call, thus letting first > > > frames in the stream to be lost. This of course cannot be done in case > > > of single-frame capture. > > > > > > To make a long story short, it would be useful in my case to have the > > > ability to return error codes as per VIDIOC_STREAMON through buf_queue > > > in the driver (when the first buffer is queued). > > > At the moment mainly EPIPE comes to my mind. This error code has no > > > meaning in the API for QBUF though. Should the pipeline be started from > > > buf_queue > > > > Hmm, the pipeline validation could still be done in start_streaming() > > so we can return any EPIPE error from there directly and effectively > > in VIDIOC_STREAMON. > > That's correct, and that's what the OMAP3 ISP driver does. > > > So the only remaining errors are those related to I2C communication etc. > > when streaming is actually enabled in the subdev. > > buf_queue is called with a spinlock help, so you can't perform I2C > communication there. In videobuf2 buf_queue() IS NOT called with any spinlock held. buf_queue can call functions that require sleeping. This makes a lot of sense especially for drivers that need to perform a lot of operations for enabling/disabling hardware. I remember we discussed your solution where you wanted to add a spinlock for calling buf_queue. This case shows one more reason not go that way. :) AFAIR buf_queue callback in old videobuf was called with spinlock held. I agree that we definitely need more documentation for vb2 and clarification what is allowed in each callback... Best regards -- Marek Szyprowski Samsung Poland R&D Center -- 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
