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 <[email protected]>
---
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);
+
return 0;
}
--
2.35.3
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 <[email protected]>
> ---
> 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 ?
> return 0;
> }
>
--
Regards,
Laurent Pinchart
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 <[email protected]>
> > ---
> > 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.
thanks,
greg k-h
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 <[email protected]>
> > > ---
> > > 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