Le jeudi 2 ao?t 2012 09:35:58 Hans Verkuil, vous avez ?crit : > On Wed August 1 2012 22:49:57 R?mi Denis-Courmont wrote: > > > What about using the CREATE_BUFS ioctl to add new MMAP buffers at > > > runtime ? > > > > Does CREATE_BUFS always work while already streaming has already started? > > If it depends on the driver, it's kinda helpless. > > Yes, it does. It's one of the reasons it exists in the first place. But > there are currently only a handful of drivers that implement it. I hope > that as more and more drivers are converted to vb2 that the availability > of create_bufs will increase.
That's contradictory. If most drivers do not support it, then it won't work during streaming. > > What's the guaranteed minimum buffer count? It seems in any case, MMAP > > has a hard limit of 32 buffers (at least videobuf2 has), though one > > might argue this should be more than enough. > > Minimum or maximum? The maximum is 32, that's hardcoded in the V4L2 core. > Although drivers may force a lower maximum if they want. I have no idea > whether there are drivers that do that. There probably are. The smallest of the maxima of all drivers. > The minimum is usually between 1 and 3, depending on hardware limitations. And that's clearly insufficient without memory copy to userspace buffers. It does not seem to me that CREATE_BUFS+MMAP is a useful replacement for REQBUFS+USERBUF then. -- R?mi Denis-Courmont http://www.remlab.net/ http://fi.linkedin.com/in/remidenis
