Hello Sakari, On 07/20/2016 09:20 AM, Sakari Ailus wrote: > Hi Javier, > > On Fri, Jul 15, 2016 at 12:26:06PM -0400, Javier Martinez Canillas wrote: >> The buffer planes' dma-buf are currently mapped when buffers are queued >> from userspace but it's more appropriate to do the mapping when buffers >> are queued in the driver since that's when the actual DMA operation are >> going to happen. >> >> Suggested-by: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx> >> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx> >> >> --- >> >> Hello, >> >> A side effect of this change is that if the dmabuf map fails for some >> reasons (i.e: a driver using the DMA contig memory allocator but CMA >> not being enabled), the fail will no longer happen on VIDIOC_QBUF but >> later (i.e: in VIDIOC_STREAMON). >> >> I don't know if that's an issue though but I think is worth mentioning. > > I have the same question has Hans --- why? > Yes, sorry for missing this information. Nicolas already explained a little bit but the context is that I want to add dma-buf fence support to videobuf2, and currently the dma-buf is unmapped in VIDIOC_DQBUF. But with dma-buf fence, the idea is to be able to dequeue a buffer even when the driver has not yet finished processing the buffer. So the dma-buf needs to be mapped until vb2_buffer_done() when the driver is done processing the vb2, and is able to signal the pending fence. Since the unmapping was going to be delayed to vb2_buffer_done(), I thought it would make sense to also move the mapping closer to when is really going to be used and that's why I moved it to __enqueue_in_driver() in this patch. But I didn't know that user-space was using the dma-buf map as a way to know if the dma-buf will be compatible and fallback to a different streaming I/O method if that's not the case. So $SUBJECT is wrong if it prevents user-space to recover gracefully from a dma-buf mapping failure. In any case, only delaying the unmapping is needed to support fence and doing the map early in VIDIOC_QBUF is not an issue. > I rather think we should keep the buffers mapped all the time. That'd > require a bit of extra from the DMA-BUF framework I suppose, to support > streaming mappings. > Interesting, I can take a look to this possibility after adding the dma-buf fence support. Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America -- 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
