On Wed, Aug 26, 2015 at 04:31:50PM -0400, Jerome Glisse wrote: > On Wed, Aug 26, 2015 at 03:44:52PM -0400, Konrad Rzeszutek Wilk wrote: > > On Wed, Aug 26, 2015 at 03:26:42PM -0400, Jerome Glisse wrote: > > > On Wed, Aug 26, 2015 at 03:02:31PM -0400, Konrad Rzeszutek Wilk wrote: > > > > On Wed, Aug 26, 2015 at 02:52:02PM -0400, jglisse at redhat.com wrote: > > > > > From: Jérôme Glisse <jglisse at redhat.com> > > > > > > > > > > Some device like GPU do things differently if swiotlb is in use. We > > > > > use to rely on swiotlb_nr_tbl() to know if swiotlb was enabled or not > > > > > but this is unreliable. Patch add a simple helpers to check if any of > > > > > > > > Why is it unreliable? > > > > > > Alex reported on irc that swiotlb_nr_tbl() returns non zero even if > > > swiotlb > > > is disabled. This seems to be due to > > > ac2cbab21f318e19bc176a7f38a120cec835220f > > > which cleanup swiotlb init and always allocate default size. Which i > > > believe > > > is a waste of memory. So we need to add a real helper to know if swiotlb > > > is > > > in use or not and we should not rely on expectation of some swiotlb value. > > > > Ah right, that patch. That should have been part of the description > > I believe. > > > > > > > > > > > > > > the dma_ops associated with a device points to the swiotlb functions, > > > > > making swiotlb check reliable for a device. > > > > > > > > > > Signed-off-by: Jérôme Glisse <jglisse at redhat.com> > > > > > Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com> > > > > > Cc: Alex Deucher <alexander.deucher at amd.com> > > > > > Cc: Ben Skeggs <bskeggs at redhat.com> > > > > > Cc: Dave Airlie <airlied at redhat.com> > > > > > Cc: lkml at vger.kernel.org > > > > > Cc: Daniel Vetter <daniel.vetter at intel.com> > > > > > --- > > > > > include/linux/dma-mapping.h | 18 ++++++++++++++++++ > > > > > 1 file changed, 18 insertions(+) > > > > > > > > > > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > > > > > index ac07ff0..eac911e 100644 > > > > > --- a/include/linux/dma-mapping.h > > > > > +++ b/include/linux/dma-mapping.h > > > > > @@ -314,4 +314,22 @@ static inline int dma_mmap_writecombine(struct > > > > > device *dev, > > > > > #define dma_unmap_len_set(PTR, LEN_NAME, VAL) do { } while (0) > > > > > #endif > > > > > > > > > > + > > > > > +#ifdef CONFIG_SWIOTLB > > > > > +static inline bool swiotlb_in_use(struct device *dev) > > > > > +{ > > > > > + struct dma_map_ops *ops = get_dma_ops(dev); > > > > > + > > > > > + return (ops->map_sg == swiotlb_map_sg_attrs || > > > > > + ops->unmap_sg == swiotlb_unmap_sg_attrs || > > > > > + ops->map_page == swiotlb_map_page); > > > > > > > > That won't work. What if we use xen-swiotlb which has different function > > > > names? > > > > > > I didn't thought about xen, always doing things differently, i think xen > > > is > > > just a matter of also testing for the xen function. I just wanted to have > > > the helper in common code and only rely on common things, instead of > > > having > > > to add a per arch helper. > > > > There has to be a better way. Perhaps you can expand SWIOTLB to actually > > check if it is in use? > > This would require per arch modifications which is what i was trying to avoid.
How? If you modify 'swiotlb_nr_tbl' to return true only if it has been used then the modifications are only in the lib/swiotlb.c ? > > Cheers, > Jérôme