On 29/10/2020 04:22, Christoph Hellwig wrote:

On Wed, Oct 28, 2020 at 06:00:29PM +1100, Alexey Kardashevskiy wrote:

quoted

At the moment we allow bypassing DMA ops only when we can do this for
the entire RAM. However there are configs with mixed type memory
where we could still allow bypassing IOMMU in most cases;
POWERPC with persistent memory is one example.

This adds an arch hook to determine where bypass can still work and
we invoke direct DMA API. The following patch checks the bus limit
on POWERPC to allow or disallow direct mapping.

This adds a CONFIG_ARCH_HAS_DMA_SET_MASK config option to make arch_xxxx
hooks no-op by default.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
  kernel/dma/mapping.c | 24 ++++++++++++++++++++----
  kernel/dma/Kconfig   |  4 ++++
  2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 51bb8fa8eb89..a0bc9eb876ed 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c

@@ -137,6 +137,18 @@ static inline bool dma_map_direct(struct device *dev,
  	return dma_go_direct(dev, *dev->dma_mask, ops);
  }
  
+#ifdef CONFIG_ARCH_HAS_DMA_MAP_DIRECT
+bool arch_dma_map_page_direct(struct device *dev, phys_addr_t addr);
+bool arch_dma_unmap_page_direct(struct device *dev, dma_addr_t dma_handle);
+bool arch_dma_map_sg_direct(struct device *dev, struct scatterlist *sg, int nents);
+bool arch_dma_unmap_sg_direct(struct device *dev, struct scatterlist *sg, int nents);
+#else
+#define arch_dma_map_page_direct(d, a) (0)
+#define arch_dma_unmap_page_direct(d, a) (0)
+#define arch_dma_map_sg_direct(d, s, n) (0)
+#define arch_dma_unmap_sg_direct(d, s, n) (0)
+#endif

A bunch of overly long lines here.  Except for that this looks ok to me.
If you want me to queue up the series I can just fix it up.

I thought 100 is the new limit since 
https://lkml.org/lkml/2020/5/29/1038 (yeah that mentioned some Christoph 
:) ) and having these multiline does not make a huge difference but feel 
free fixing them up.

Are you going to take both patches? Do you need mpe's ack? Thanks,


-- 
Alexey