On 01/20/15 13:59, Laurent Pinchart wrote: > 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. So we can safely use videobuf2-vmalloc, right? Regards, Hans > >>>> 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. > -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
