This looks interesting. I suspect it is going to blow up in quite a few places, so maybe at least for now it might make sense to have a separate config option?
On Tue, Apr 24, 2018 at 05:12:19PM +0100, Robin Murphy wrote: > Drivers/subsystems creating scatterlists for DMA should be taking care > to respect the scatter-gather limitations of the appropriate device, as > described by dma_parms. A DMA API implementation cannot feasibly split > a scatterlist into *more* entries than originally passed, so it is not > well defined what they should do when given a segment larger than the > limit they are also required to respect. > > Conversely, devices which are less limited than the rather conservative > defaults, or indeed have no limitations at all (e.g. GPUs with their own > internal MMU), should be encouraged to set appropriate dma_parms, as > they may get more efficient DMA mapping performance out of it. > > Signed-off-by: Robin Murphy <[email protected]> > --- > lib/dma-debug.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/lib/dma-debug.c b/lib/dma-debug.c > index 7f5cdc1e6b29..9f158941004d 100644 > --- a/lib/dma-debug.c > +++ b/lib/dma-debug.c > @@ -1293,6 +1293,30 @@ static void check_sync(struct device *dev, > put_hash_bucket(bucket, &flags); > } > > +static void check_sg_segment(struct device *dev, struct scatterlist *sg) > +{ > + unsigned int max_seg = dma_get_max_seg_size(dev); > + dma_addr_t start, end, boundary = dma_get_seg_boundary(dev); > + > + /* > + * Either the driver forgot to set dma_parms appropriately, or > + * whoever generated the list forgot to check them. > + */ > + if (sg->length > max_seg) > + err_printk(dev, NULL, "DMA-API: mapping sg segment longer than > device claims to support [len=%u] [max=%u]\n", > + sg->length, max_seg); > + /* > + * In some cases this could potentially be the DMA API > + * implementation's fault, but it would usually imply that > + * the scatterlist was built inappropriately to begin with. > + */ > + start = sg_dma_address(sg); > + end = start + sg_dma_len(sg) - 1; > + if ((start ^ end) & ~boundary) > + err_printk(dev, NULL, "DMA-API: mapping sg segment across > boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n", > + start, end, boundary); > +} > + > void debug_dma_map_page(struct device *dev, struct page *page, size_t offset, > size_t size, int direction, dma_addr_t dma_addr, > bool map_single) > @@ -1423,6 +1447,8 @@ void debug_dma_map_sg(struct device *dev, struct > scatterlist *sg, > check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s)); > } > > + check_sg_segment(dev, s); > + > add_dma_entry(entry); > } > } > -- > 2.17.0.dirty ---end quoted text---
