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@redhat.com wrote:
From: Jérôme Glisse jglisse@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.
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@redhat.com Cc: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Ben Skeggs bskeggs@redhat.com Cc: Dave Airlie airlied@redhat.com Cc: lkml@vger.kernel.org Cc: Daniel Vetter daniel.vetter@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.
Cheers, Jérôme