On Fri, 10 Jun 2022 10:57:40 +0200, Greg Kroah-Hartman wrote: > > On Thu, Jun 09, 2022 at 12:18:30PM +0300, Laurent Pinchart wrote: > > Hi Takashi, > > > > (CC'ing Greg and the linux-usb mailing list) > > > > Thank you for the patch. > > > > On Thu, Jun 09, 2022 at 10:22:46AM +0200, Takashi Iwai wrote: > > > As default, the DMA max segment size is set to 64k, and uvcvideo may > > > overflow that size easily, resulting in a warning like: > > > > > > DMA-API: xhci_hcd 0000:00:14.0: mapping sg segment longer than device claims to support [len=98304] [max=65536] > > > > > > Explicitly set up the DMA max segment size for avoiding spurious kernel > > > warnings. > > > > > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> > > > --- > > > drivers/media/usb/uvc/uvc_video.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > > > index 1b4cc934109e..25aa6e6a6906 100644 > > > --- a/drivers/media/usb/uvc/uvc_video.c > > > +++ b/drivers/media/usb/uvc/uvc_video.c > > > @@ -2160,6 +2160,8 @@ int uvc_video_init(struct uvc_streaming *stream) > > > for_each_uvc_urb(uvc_urb, stream) > > > INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work); > > > > > > + dma_set_max_seg_size(uvc_stream_to_dmadev(stream), UINT_MAX); > > > + > > > > uvc_stream_to_dmadev() returns the pointer to the HCD's struct device, > > which is shared between all drivers on the bus. Is it really fine for a > > USB device driver to change the maximum segment size of the HCD device > > directly ? > > Ick, no! That feels wrong, it should only change things for that one > specific device, not all devices on that bus. Hrm, indeed, that points to the HCD. This made me wonder, though, whether the current usage of dma_*sgtable() with that device is OK or not. The warning came from that code path, after all... Takashi
