On Fri, 20 Apr 2012 10:41:37 +0200, Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx> wrote: >> Am I understanding wrong or are you saying that you want to drop userptr >> from V4L2 API in long-term? If so, why? > > Dropping userptr is just some brainstorming idea. > It was found out that userptr is not a good mean > for buffer exchange between to two devices. I can believe that. But I am also inclined to believe that DMABUF is targetted at device-to-device transfer, while USERPTR is targetted at device-to-user (or user-to-device) transfers. Are you saying applications should use DMABUF and memory map the buffers? Or would you care to explain how DMABUF addresses the problem space of USERPTR? > The USERPTR simplifies userspace code but introduce > a lot of complexity problems for the kernel drivers > and frameworks. It is not only a simplification. In some cases, USERPTR is the only I/O method that supports zero copy in pretty much any circumstance. When the user cannot reliably predict the maximum number of required buffers, predicts a value larger than the device will negotiate, or needs buffers to outlive STREAMOFF (?), MMAP requires memory copying. USERPTR does not. Now, I do realize that some devices cannot support USERPTR efficiently, then they should not support USERPTR. But for those devices that can, it seems quite a nice performance enhancement. -- Rémi Denis-Courmont Sent from my collocated server -- 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
