Hi Rémi, On Thursday 02 August 2012 09:56:43 Rémi Denis-Courmont wrote: > Le jeudi 2 août 2012 09:35:58 Hans Verkuil, vous avez écrit : > > On Wed August 1 2012 22:49:57 Rémi 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. That's the minimum number of buffers *required* by the hardware. You can add up to 32 buffers, I'm not aware of any driver that would prevent that. > It does not seem to me that CREATE_BUFS+MMAP is a useful replacement for > REQBUFS+USERBUF then. -- 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
