Re: [PATCH 09/16] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg

[Jason Gunthorpe]

On Tue, Apr 27, 2021 at 04:33:51PM -0300, Jason Gunthorpe wrote:
> On Thu, Apr 08, 2021 at 11:01:16AM -0600, Logan Gunthorpe wrote:
> > Add PCI P2PDMA support for dma_direct_map_sg() so that it can map
> > PCI P2PDMA pages directly without a hack in the callers. This allows
> > for heterogeneous SGLs that contain both P2PDMA and regular pages.
> > 
> > SGL segments that contain PCI bus addresses are marked with
> > sg_mark_pci_p2pdma() and are ignored when unmapped.
> > 
> > Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> >  kernel/dma/direct.c | 25 ++++++++++++++++++++++---
> >  1 file changed, 22 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index 002268262c9a..108dfb4ecbd5 100644
> > +++ b/kernel/dma/direct.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/vmalloc.h>
> >  #include <linux/set_memory.h>
> >  #include <linux/slab.h>
> > +#include <linux/pci-p2pdma.h>
> >  #include "direct.h"
> >  
> >  /*
> > @@ -387,19 +388,37 @@ void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl,
> >  	struct scatterlist *sg;
> >  	int i;
> >  
> > -	for_each_sg(sgl, sg, nents, i)
> > +	for_each_sg(sgl, sg, nents, i) {
> > +		if (sg_is_pci_p2pdma(sg)) {
> > +			sg_unmark_pci_p2pdma(sg);
> 
> This doesn't seem nice, the DMA layer should only alter the DMA
> portion of the SG, not the other portions. Is it necessary?

Oh, I got it completely wrong what this is for.

This should be named sg_dma_mark_pci_p2p() and similar for other
functions to make it clear it is part of the DMA side of the SG
interface (eg it is like sg_dma_address, sg_dma_len, etc)

Jason