[RFC PATCH v2 06/11] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg

[Logan Gunthorpe]

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 at deltatee.com>
---
 kernel/dma/direct.c  | 35 ++++++++++++++++++++++++++++++++---
 kernel/dma/mapping.c | 13 ++++++++++---
 2 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 002268262c9a..f326d32062dd 100644
--- a/kernel/dma/direct.c
+++ 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 +388,47 @@ 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))
+			continue;
+
 		dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir,
 			     attrs);
+	}
 }
 #endif
 
 int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
 		enum dma_data_direction dir, unsigned long attrs)
 {
-	int i;
+	struct dev_pagemap *pgmap = NULL;
+	int i, map = -1, ret = 0;
 	struct scatterlist *sg;
+	u64 bus_off;
 
 	for_each_sg(sgl, sg, nents, i) {
+		if (is_pci_p2pdma_page(sg_page(sg))) {
+			if (sg_page(sg)->pgmap != pgmap) {
+				pgmap = sg_page(sg)->pgmap;
+				map = pci_p2pdma_dma_map_type(dev, pgmap);
+				bus_off = pci_p2pdma_bus_offset(sg_page(sg));
+			}
+
+			if (map < 0) {
+				sg->dma_address = DMA_MAPPING_ERROR;
+				ret = -EREMOTEIO;
+				goto out_unmap;
+			}
+
+			if (map) {
+				sg->dma_address = sg_phys(sg) + sg->offset -
+					bus_off;
+				sg_dma_len(sg) = sg->length;
+				sg_mark_pci_p2pdma(sg);
+				continue;
+			}
+		}
+
 		sg->dma_address = dma_direct_map_page(dev, sg_page(sg),
 				sg->offset, sg->length, dir, attrs);
 		if (sg->dma_address == DMA_MAPPING_ERROR)
@@ -411,7 +440,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
 
 out_unmap:
 	dma_direct_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
-	return 0;
+	return ret;
 }
 
 dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index b6a633679933..adc1a83950be 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -178,8 +178,15 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
 EXPORT_SYMBOL(dma_unmap_page_attrs);
 
 /*
- * dma_maps_sg_attrs returns 0 on error and > 0 on success.
- * It should never return a value < 0.
+ * dma_maps_sg_attrs returns 0 on any resource error and > 0 on success.
+ *
+ * If 0 is returned, the mapping can be retried and will succeed once
+ * sufficient resources are available.
+ *
+ * If there are P2PDMA pages in the scatterlist then this function may
+ * return -EREMOTEIO to indicate that the pages are not mappable by the
+ * device. In this case, an error should be returned for the IO as it
+ * will never be successfully retried.
  */
 int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 		enum dma_data_direction dir, unsigned long attrs)
@@ -197,7 +204,7 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 		ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
 	else
 		ents = ops->map_sg(dev, sg, nents, dir, attrs);
-	BUG_ON(ents < 0);
+
 	debug_dma_map_sg(dev, sg, nents, ents, dir);
 
 	return ents;
-- 
2.20.1