Hello Hans, On 07/20/2016 10:12 AM, Hans Verkuil wrote: > On 07/20/2016 04:06 PM, Javier Martinez Canillas wrote: >> 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. > > OK. I've rejected this patch. I understand the DQBUF part and I happily accept Ok, thanks. > a patch for that. But the other side should be left as-is. The TODO comment > should probably be dropped, now that I think about it. > I can post such a patch, do you want me to also add a comment about why is done in QBUF instead of when the buffer is queued in the driver (e.g: that user-space is able to recover in QBUF but no in STREAMON) or just removing it and mention that in the commit message is enough? > Regards, > > Hans > 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
