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

Logan Gunthorpe
2021-03-11T23:48:50Z

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@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