Commit 2df55d9e authored by Thomas Hellström's avatar Thomas Hellström
Browse files

drm/xe: Support pcie p2p dma as a fast interconnect 



Mimic the dma-buf method using dma_[map|unmap]_resource to map
for pcie-p2p dma.

There's an ongoing area of work upstream to sort out how this best
should be done. One method proposed is to add an additional
pci_p2p_dma_pagemap aliasing the device_private pagemap and use
the corresponding pci_p2p_dma_pagemap page as input for
dma_map_page(). However, that would incur double the amount of
memory and latency to set up the drm_pagemap and given the huge
amount of memory present on modern GPUs, that would really not work.
Hence the simple approach used in this patch.

v2:
- Simplify xe_page_to_pcie(). (Matt Brost)

Signed-off-by: default avatarThomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: default avatarMatthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251219113320.183860-17-thomas.hellstrom@linux.intel.com
parent dff547e1

drivers/gpu/drm/xe/xe_svm.c

+31 −3
Original line number Diff line number Diff line
@@ -3,6 +3,8 @@ 
 * Copyright © 2024 Intel Corporation

 */



#include <linux/pci-p2pdma.h>



#include <drm/drm_drv.h>

#include <drm/drm_managed.h>

#include <drm/drm_pagemap.h>
@@ -441,6 +443,14 @@ static u64 xe_page_to_dpa(struct page *page) 
	return dpa;

}



static u64 xe_page_to_pcie(struct page *page)

{

	struct xe_pagemap *xpagemap = xe_page_to_pagemap(page);

	struct xe_vram_region *vr = xe_pagemap_to_vr(xpagemap);



	return xe_page_to_dpa(page) - vr->dpa_base + vr->io_start;

}



enum xe_svm_copy_dir {

	XE_SVM_COPY_TO_VRAM,

	XE_SVM_COPY_TO_SRAM,
@@ -804,7 +814,10 @@ static bool xe_has_interconnect(struct drm_pagemap_peer *peer1, 
	struct device *dev1 = xe_peer_to_dev(peer1);

	struct device *dev2 = xe_peer_to_dev(peer2);



	return dev1 == dev2;

	if (dev1 == dev2)

		return true;



	return pci_p2pdma_distance(to_pci_dev(dev1), dev2, true) >= 0;

}



static DRM_PAGEMAP_OWNER_LIST_DEFINE(xe_owner_list);
@@ -1577,13 +1590,27 @@ xe_drm_pagemap_device_map(struct drm_pagemap *dpagemap, 
		addr = xe_page_to_dpa(page);

		prot = XE_INTERCONNECT_VRAM;

	} else {

		addr = DMA_MAPPING_ERROR;

		prot = 0;

		addr = dma_map_resource(dev,

					xe_page_to_pcie(page),

					PAGE_SIZE << order, dir,

					DMA_ATTR_SKIP_CPU_SYNC);

		prot = XE_INTERCONNECT_P2P;

	}



	return drm_pagemap_addr_encode(addr, prot, order, dir);

}



static void xe_drm_pagemap_device_unmap(struct drm_pagemap *dpagemap,

					struct device *dev,

					struct drm_pagemap_addr addr)

{

	if (addr.proto != XE_INTERCONNECT_P2P)

		return;



	dma_unmap_resource(dev, addr.addr, PAGE_SIZE << addr.order,

			   addr.dir, DMA_ATTR_SKIP_CPU_SYNC);

}



static void xe_pagemap_destroy_work(struct work_struct *work)

{

	struct xe_pagemap *xpagemap = container_of(work, typeof(*xpagemap), destroy_work);
@@ -1620,6 +1647,7 @@ static void xe_pagemap_destroy(struct drm_pagemap *dpagemap, bool from_atomic_or 


static const struct drm_pagemap_ops xe_drm_pagemap_ops = {

	.device_map = xe_drm_pagemap_device_map,

	.device_unmap = xe_drm_pagemap_device_unmap,

	.populate_mm = xe_drm_pagemap_populate_mm,

	.destroy = xe_pagemap_destroy,

};

drivers/gpu/drm/xe/xe_svm.h

+1 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#include <drm/drm_pagemap_util.h>



#define XE_INTERCONNECT_VRAM DRM_INTERCONNECT_DRIVER

#define XE_INTERCONNECT_P2P (XE_INTERCONNECT_VRAM + 1)



struct drm_device;

struct drm_file;