diff mbox series

[v2,15/22] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg

Message ID 20210513223203.5542-16-logang@deltatee.com (mailing list archive)
State New
Headers show
Series Add new DMA mapping operation for P2PDMA | expand

Commit Message

Logan Gunthorpe May 13, 2021, 10:31 p.m. UTC
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.

A P2PDMA page may have three possible outcomes when being mapped:
  1) If the data path between the two devices doesn't go through the
     root port, then it should be mapped with a PCI bus address
  2) If the data path goes through the host bridge, it should be mapped
     normally, as though it were a CPU physical address
  3) It is not possible for the two devices to communicate and thus
     the mapping operation should fail (and it will return -EREMOTEIO).

SGL segments that contain PCI bus addresses are marked with
sg_dma_mark_pci_p2pdma() and are ignored when unmapped.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 kernel/dma/direct.c | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

Comments

Christoph Hellwig May 14, 2021, 1:57 p.m. UTC | #1
> +	for_each_sg(sgl, sg, nents, i) {
> +		if (sg_is_dma_pci_p2pdma(sg)) {
> +			sg_dma_unmark_pci_p2pdma(sg);
> +		} else  {

Double space here.  We also don't really need the curly braces to start
with.

> +	struct pci_p2pdma_map_state p2pdma_state = {};
> +	enum pci_p2pdma_map_type map;
>  	struct scatterlist *sg;
> +	int i, ret;
>  
>  	for_each_sg(sgl, sg, nents, i) {
> +		if (is_pci_p2pdma_page(sg_page(sg))) {
> +			map = pci_p2pdma_map_segment(&p2pdma_state, dev, sg);
> +			switch (map) {

Why not just:

			switch (pci_p2pdma_map_segment(&p2pdma_state, dev,
					sg)) {

(even better with a shorter name for p2pdma_state so that it all fits on
a single line)?

> +			case PCI_P2PDMA_MAP_BUS_ADDR:
> +				continue;
> +			case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> +				/*
> +				 * Mapping through host bridge should be
> +				 * mapped normally, thus we do nothing
> +				 * and continue below.
> +				 */

I have a bit of a hard time parsing this comment.

> +		if (sg->dma_address == DMA_MAPPING_ERROR) {
> +			ret = -EINVAL;
>  			goto out_unmap;
> +		}
>  		sg_dma_len(sg) = sg->length;
>  	}
>  
> @@ -411,7 +443,7 @@ 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 -EINVAL;
> +	return ret;

Maybe just initialize ret to -EINVAL at declaration time to simplify this
a bit?
Logan Gunthorpe May 14, 2021, 4:17 p.m. UTC | #2
On 2021-05-14 7:57 a.m., Christoph Hellwig wrote:
>> +	for_each_sg(sgl, sg, nents, i) {
>> +		if (sg_is_dma_pci_p2pdma(sg)) {
>> +			sg_dma_unmark_pci_p2pdma(sg);
>> +		} else  {
> 
> Double space here.  We also don't really need the curly braces to start
> with.
> 
>> +	struct pci_p2pdma_map_state p2pdma_state = {};
>> +	enum pci_p2pdma_map_type map;
>>  	struct scatterlist *sg;
>> +	int i, ret;
>>  
>>  	for_each_sg(sgl, sg, nents, i) {
>> +		if (is_pci_p2pdma_page(sg_page(sg))) {
>> +			map = pci_p2pdma_map_segment(&p2pdma_state, dev, sg);
>> +			switch (map) {
> 
> Why not just:
> 
> 			switch (pci_p2pdma_map_segment(&p2pdma_state, dev,
> 					sg)) {
> 
> (even better with a shorter name for p2pdma_state so that it all fits on
> a single line)?
> 
>> +			case PCI_P2PDMA_MAP_BUS_ADDR:
>> +				continue;
>> +			case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
>> +				/*
>> +				 * Mapping through host bridge should be
>> +				 * mapped normally, thus we do nothing
>> +				 * and continue below.
>> +				 */
> 
> I have a bit of a hard time parsing this comment.
> 
>> +		if (sg->dma_address == DMA_MAPPING_ERROR) {
>> +			ret = -EINVAL;
>>  			goto out_unmap;
>> +		}
>>  		sg_dma_len(sg) = sg->length;
>>  	}
>>  
>> @@ -411,7 +443,7 @@ 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 -EINVAL;
>> +	return ret;
> 
> Maybe just initialize ret to -EINVAL at declaration time to simplify this
> a bit?
>

All fair points, will fix in v3.

Logan
diff mbox series

Patch

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 803ee9321170..567dac942e89 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"
 
 /*
@@ -381,29 +382,60 @@  void dma_direct_sync_sg_for_cpu(struct device *dev,
 		arch_sync_dma_for_cpu_all();
 }
 
+/*
+ * Unmaps segments, except for ones marked as pci_p2pdma which do not
+ * require any further action as they contain a bus address.
+ */
 void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl,
 		int nents, enum dma_data_direction dir, unsigned long attrs)
 {
 	struct scatterlist *sg;
 	int i;
 
-	for_each_sg(sgl, sg, nents, i)
-		dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir,
-			     attrs);
+	for_each_sg(sgl, sg, nents, i) {
+		if (sg_is_dma_pci_p2pdma(sg)) {
+			sg_dma_unmark_pci_p2pdma(sg);
+		} else  {
+			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 pci_p2pdma_map_state p2pdma_state = {};
+	enum pci_p2pdma_map_type map;
 	struct scatterlist *sg;
+	int i, ret;
 
 	for_each_sg(sgl, sg, nents, i) {
+		if (is_pci_p2pdma_page(sg_page(sg))) {
+			map = pci_p2pdma_map_segment(&p2pdma_state, dev, sg);
+			switch (map) {
+			case PCI_P2PDMA_MAP_BUS_ADDR:
+				continue;
+			case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
+				/*
+				 * Mapping through host bridge should be
+				 * mapped normally, thus we do nothing
+				 * and continue below.
+				 */
+				break;
+			default:
+				ret = -EREMOTEIO;
+				goto out_unmap;
+			}
+		}
+
 		sg->dma_address = dma_direct_map_page(dev, sg_page(sg),
 				sg->offset, sg->length, dir, attrs);
-		if (sg->dma_address == DMA_MAPPING_ERROR)
+		if (sg->dma_address == DMA_MAPPING_ERROR) {
+			ret = -EINVAL;
 			goto out_unmap;
+		}
 		sg_dma_len(sg) = sg->length;
 	}
 
@@ -411,7 +443,7 @@  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 -EINVAL;
+	return ret;
 }
 
 dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,