| Message ID | 20180730163824.10064-9-hch@lst.de (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [01/20] kernel/dma/direct: take DMA offset into account in dma_direct_supported | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | next/apply_patch Successfully applied |
| snowpatch_ozlabs/checkpatch | success | Test checkpatch on branch next |
It turns out cxl actually uses it. So for now skip this patch, although random code in drivers messing with dma ops will need to be sorted out sooner or later.
On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote: > It turns out cxl actually uses it. So for now skip this patch, > although random code in drivers messing with dma ops will need to > be sorted out sooner or later. CXL devices are "special", they bypass the classic iommu in favor of allowing the device to operate using the main processor page tables using an MMU context (so basically the device can use userspace addresses directly), akin to ATS. I think the code currently uses the nommu ops as a way to do a simple kernel mapping for kernel drivers using CXL (not userspace stuff) though. Ben.
On Thu, Aug 09, 2018 at 10:01:16AM +1000, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote: > > It turns out cxl actually uses it. So for now skip this patch, > > although random code in drivers messing with dma ops will need to > > be sorted out sooner or later. > > CXL devices are "special", they bypass the classic iommu in favor of > allowing the device to operate using the main processor page tables > using an MMU context (so basically the device can use userspace > addresses directly), akin to ATS. > > I think the code currently uses the nommu ops as a way to do a simple > kernel mapping for kernel drivers using CXL (not userspace stuff) > though. Its still a horrible idea to have this in drivers/, we need some core API to mediate this behavior. Also if the device supports using virtual addresses dma_nommu_ops seems wrong as it won't do the right thing for e.g. vmalloc addresses not mapped into the kernel linear mapping (which I guess can't currently happen on powerpc, but still..)
On Wed, 2018-08-22 at 08:45 +0200, Christoph Hellwig wrote: > On Thu, Aug 09, 2018 at 10:01:16AM +1000, Benjamin Herrenschmidt wrote: > > On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote: > > > It turns out cxl actually uses it. So for now skip this patch, > > > although random code in drivers messing with dma ops will need to > > > be sorted out sooner or later. > > > > CXL devices are "special", they bypass the classic iommu in favor of > > allowing the device to operate using the main processor page tables > > using an MMU context (so basically the device can use userspace > > addresses directly), akin to ATS. > > > > I think the code currently uses the nommu ops as a way to do a simple > > kernel mapping for kernel drivers using CXL (not userspace stuff) > > though. > > Its still a horrible idea to have this in drivers/, we need some > core API to mediate this behavior. Also if the device supports > using virtual addresses dma_nommu_ops seems wrong as it won't do > the right thing for e.g. vmalloc addresses not mapped into the > kernel linear mapping (which I guess can't currently happen on > powerpc, but still..) You are right it won't do the right thing, but neither will standard DMA ops, will they ? Drivers know not to try to dma_map vmalloc addresses without first getting the underlying page, nothing unusal there. Yes I agree having this in drivers somewhat sucks though. Cheers, Ben.
diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c index dbfc7056d7df..3939589aab04 100644 --- a/arch/powerpc/kernel/dma.c +++ b/arch/powerpc/kernel/dma.c @@ -286,7 +286,6 @@ const struct dma_map_ops dma_nommu_ops = { .sync_sg_for_device = dma_nommu_sync_sg, #endif }; -EXPORT_SYMBOL(dma_nommu_ops); int dma_set_coherent_mask(struct device *dev, u64 mask) {
Signed-off-by: Christoph Hellwig <hch@lst.de> --- arch/powerpc/kernel/dma.c | 1 - 1 file changed, 1 deletion(-)