Re: [PATCH] dma-mapping: direct: fix missing mapping for THRU_HOST_BRIDGE segments

[Leon Romanovsky <leon@kernel.org>]

On Wed, Jun 03, 2026 at 06:25:22PM +0200, Marek Szyprowski wrote:
> On 03.06.2026 03:37, lirongqing wrote:
> > From: Li RongQing <lirongqing@baidu.com>
> >
> > In dma_direct_map_sg(), the case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE
> > incorrectly used 'break' instead of falling through to MAP_NONE.
> > As a result, segments traversing the host bridge skipped the required
> > dma_direct_map_phys() call entirely, leaving sg->dma_address
> > uninitialized and leading to DMA failures. Fix this by using
> > 'fallthrough;'.
> >
> > Fixes: a25e7962db0d79 ("PCI/P2PDMA: Refactor the p2pdma mapping helpers")
> > Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> 
> Applied to dma-mapping-fixes, thanks!

The change looks correct, but it will be better if this change will
improve d0d08f4bd7f6 ("dma-direct: Fix missing sg_dma_len assignment in
P2PDMA bus mappings") too.

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index ec887f443741..e98b6547c950 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -489,9 +489,8 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
                case PCI_P2PDMA_MAP_BUS_ADDR:
                        sg->dma_address = pci_p2pdma_bus_addr_map(
                                p2pdma_state.mem, sg_phys(sg));
-                       sg_dma_len(sg) = sg->length;
                        sg_dma_mark_bus_address(sg);
-                       continue;
+                       break;
                default:
                        ret = -EREMOTEIO;
                        goto out_unmap;

Thanks

> 
> 
> > ---
> >  kernel/dma/direct.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index 583c592..4391b79 100644
> > --- a/kernel/dma/direct.c
> > +++ b/kernel/dma/direct.c
> > @@ -476,7 +476,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
> >  			 * must be mapped with CPU physical address and not PCI
> >  			 * bus addresses.
> >  			 */
> > -			break;
> > +			fallthrough;
> >  		case PCI_P2PDMA_MAP_NONE:
> >  			need_sync = true;
> >  			sg->dma_address = dma_direct_map_phys(dev, sg_phys(sg),
> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>