Hi Hans, On Saturday 20 February 2010 15:00:21 Hans Verkuil wrote: > I have a few more questions regarding the streaming I/O API: > > 1) The spec mentions that the memory field should be set for VIDIOC_DQBUF. > But videobuf doesn't need it and it makes no sense to me either unless it > is for symmetry with VIDIOC_QBUF. Strictly speaking QBUF doesn't need it > either, but it is a good sanity check. > > Can I remove the statement in the spec that memory should be set for DQBUF? > The alternative is to add a check against the memory field in videobuf, but > that's rather scary. In that case I would remove it for QBUF as well, and state that the memory field must be ignored by drivers (but should they fill it when returning from QBUF/DQBUF ?) > 2) What to do with REQBUFS when called with a count of 0? Thinking it over > I agree that it shouldn't do an implicit STREAMOFF. But I do think that it > is useful to allow as a simple check whether the I/O method is supported. REQBUFS(0) should also free allocated buffers (if any). > So a count of 0 will either return an error if streaming is still in > progress or if the proposed I/O method is not supported, otherwise it will > return 0 while leaving count to 0. > > This allows one to use REQBUFS to test which I/O methods are supported by > the driver without having the driver allocating any buffers. > > This will become more important with embedded systems where almost > certainly additional I/O methods will be introduced (in particular > non-contiguous plane support). > > Currently a count of 0 will result in an error in videobuf. > > Note that drivers do not generally check for valid values of the memory > field at the moment. So that is another thing we need to improve. But > before I start working on that, I first want to know exactly how REQBUFS > should work. -- Regards, Laurent Pinchart -- 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
