Hello, On Tuesday 20 January 2015 10:30:07 Hans Verkuil wrote: > On 01/20/15 10:24, Florian Echtler wrote: > > On 19.01.2015 11:38, Hans Verkuil wrote: > >> Sorry for the delay. > > > > No problem, thanks for your feedback. > > > >>> Note: I'm intentionally using dma-contig instead of vmalloc, as the USB > >>> core apparently _will_ try to use DMA for larger bulk transfers. > >> > >> As far as I can tell from looking through the usb core code it supports > >> scatter-gather DMA, so you should at least use dma-sg rather than > >> dma-contig. Physically contiguous memory should always be avoided. > > > > OK, will this work transparently (i.e. just switch from *-contig-* to > > *-sg-*)? If not, can you suggest an example driver to use as template? > > Yes, that should pretty much be seamless. BTW, the more I think about it, > the more I am convinced that DMA will also be used by the USB core when > you use videobuf2-vmalloc. > > I've CC-ed Laurent, I think he knows a lot more about this than I do. > > Laurent, when does the USB core use DMA? What do you need to do on the > driver side to have USB use DMA when doing bulk transfers?
How USB HCD drivers map buffers for DMA is HCD-specific, but all drivers exepct ehci-tegra, max3421-hcd and musb use the default implementation usb_hcd_map_urb_for_dma() (in drivers/usb/core/hcd.c). Unless the buffer has already been mapped by the USB driver (in which case the driver will have set the URB_NO_TRANSFER_DMA_MAP flag in urb->transfer_flags and initialized the urb->transfer_dma field), the function will use dma_map_sg(), dma_map_page() or dma_map_single() depending on the buffer type (controlled through urb->sg and urb->num_sgs). DMA will thus always be used *expect* if the platform uses bounce buffers when the buffer can't be mapped directly for DMA. > >> I'm also missing a patch for the Kconfig that adds a dependency on > >> MEDIA_USB_SUPPORT and that selects VIDEOBUF2_DMA_SG. > > > > Good point, will add that. > > > >>> +err_unreg_video: > >>> + video_unregister_device(&sur40->vdev); > >>> +err_unreg_v4l2: > >>> + v4l2_device_unregister(&sur40->v4l2); > >>> > >>> err_free_buffer: > >>> kfree(sur40->bulk_in_buffer); > >>> > >>> err_free_polldev: > >>> @@ -436,6 +604,10 @@ static void sur40_disconnect(struct usb_interface > >>> *interface)>> > >> Is this a hardwired device or hotpluggable? If it is hardwired, then this > >> code is OK, but if it is hotpluggable, then this isn't good enough. > > > > It's hardwired. Out of curiosity, what would I have to change for a > > hotpluggable one? > > In that case you can't clean everything up since some application might > still have a filehandle open. You have to wait until the very last > filehandle is closed. > > >>> + i->type = V4L2_INPUT_TYPE_CAMERA; > >>> + i->std = V4L2_STD_UNKNOWN; > >>> + strlcpy(i->name, "In-Cell Sensor", sizeof(i->name)); > >> > >> Perhaps just say "Sensor" here? I'm not sure what "In-Cell" means. > > > > In-cell is referring to the concept of integrating sensor pixels > > directly with LCD pixels, I think it's what Samsung calls it. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
