On 2021-05-11 10:06 a.m., Don Dutile wrote:

On 4/8/21 1:01 PM, Logan Gunthorpe wrote:

quoted

Add a flags member to the dma_map_ops structure with one flag to
indicate support for PCI P2PDMA.

Also, add a helper to check if a device supports PCI P2PDMA.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
  include/linux/dma-map-ops.h |  3 +++
  include/linux/dma-mapping.h |  5 +++++
  kernel/dma/mapping.c        | 18 ++++++++++++++++++
  3 files changed, 26 insertions(+)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 51872e736e7b..481892822104 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h

@@ -12,6 +12,9 @@
  struct cma;
  
  struct dma_map_ops {
+	unsigned int flags;
+#define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
+

I'm not a fan of in-line define's; if we're going to add a flags field to the dma-ops
-- and logically it'd be good to have p2pdma go through the dma-ops struct --
then let's move this up in front of the dma-ops description.

Already changed for v2.

And now that the dma-ops struct is being 'opened' for p2pdma, should p2pdma ops be added
to this struct, so all this work can be mimic'd/reflected/leveraged/refactored for CXL, GenZ, etc. p2pdma in (the near?) future?

v2 no longer has a specific op for p2pdma. We are now using
dma_map_sgtable() which already has the error return we need.

I think any work to support CXL, GenZ, etc will need to be done when
they add their own support. I can't and shouldn't guess at their needs now.

Logan