drm/xe: Add drm_pagemap ops to SVM

Add support for mapping device pages to Xe SVM by attaching drm_pagemap
to a memory region, which is then linked to a GPU SVM devmem allocation.
This enables GPU SVM to derive the device page address.

v3:
 - Better commit message (Thomas)
 - New drm_pagemap.h location
v5:
 - s/xe_mem_region/xe_vram_region (Rebase)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250306012657.3505757-24-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_device_types.h

@@ -10,6 +10,7 @@
 
 #include <drm/drm_device.h>
 #include <drm/drm_file.h>
+#include <drm/drm_pagemap.h>
 #include <drm/ttm/ttm_device.h>
 
 #include "xe_devcoredump_types.h"
@@ -108,6 +109,11 @@ struct xe_vram_region {
 	void __iomem *mapping;
 	/** @pagemap: Used to remap device memory as ZONE_DEVICE */
 	struct dev_pagemap pagemap;
+	/**
+	 * @dpagemap: The struct drm_pagemap of the ZONE_DEVICE memory
+	 * pages of this tile.
+	 */
+	struct drm_pagemap dpagemap;
 	/**
 	 * @hpa_base: base host physical address
 	 *

drivers/gpu/drm/xe/xe_svm.c

@@ -288,6 +288,33 @@ static void xe_svm_garbage_collector_work_func(struct work_struct *w)
 	up_write(&vm->lock);
 }
 
+static struct xe_vram_region *page_to_vr(struct page *page)
+{
+	return container_of(page->pgmap, struct xe_vram_region, pagemap);
+}
+
+static struct xe_tile *vr_to_tile(struct xe_vram_region *vr)
+{
+	return container_of(vr, struct xe_tile, mem.vram);
+}
+
+static u64 xe_vram_region_page_to_dpa(struct xe_vram_region *vr,
+				      struct page *page)
+{
+	u64 dpa;
+	struct xe_tile *tile = vr_to_tile(vr);
+	u64 pfn = page_to_pfn(page);
+	u64 offset;
+
+	xe_tile_assert(tile, is_device_private_page(page));
+	xe_tile_assert(tile, (pfn << PAGE_SHIFT) >= vr->hpa_base);
+
+	offset = (pfn << PAGE_SHIFT) - vr->hpa_base;
+	dpa = vr->dpa_base + offset;
+
+	return dpa;
+}
+
 static const struct drm_gpusvm_ops gpusvm_ops = {
 	.range_alloc = xe_svm_range_alloc,
 	.range_free = xe_svm_range_free,
@@ -456,6 +483,32 @@ bool xe_svm_has_mapping(struct xe_vm *vm, u64 start, u64 end)
 }
 
 #if IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR)
+static struct drm_pagemap_device_addr
+xe_drm_pagemap_device_map(struct drm_pagemap *dpagemap,
+			  struct device *dev,
+			  struct page *page,
+			  unsigned int order,
+			  enum dma_data_direction dir)
+{
+	struct device *pgmap_dev = dpagemap->dev;
+	enum drm_interconnect_protocol prot;
+	dma_addr_t addr;
+
+	if (pgmap_dev == dev) {
+		addr = xe_vram_region_page_to_dpa(page_to_vr(page), page);
+		prot = XE_INTERCONNECT_VRAM;
+	} else {
+		addr = DMA_MAPPING_ERROR;
+		prot = 0;
+	}
+
+	return drm_pagemap_device_addr_encode(addr, prot, order, dir);
+}
+
+static const struct drm_pagemap_ops xe_drm_pagemap_ops = {
+	.device_map = xe_drm_pagemap_device_map,
+};
+
 /**
  * xe_devm_add: Remap and provide memmap backing for device memory
  * @tile: tile that the memory region belongs to
@@ -488,6 +541,10 @@ int xe_devm_add(struct xe_tile *tile, struct xe_vram_region *vr)
 	vr->pagemap.ops = drm_gpusvm_pagemap_ops_get();
 	vr->pagemap.owner = xe_svm_devm_owner(xe);
 	addr = devm_memremap_pages(dev, &vr->pagemap);
+
+	vr->dpagemap.dev = dev;
+	vr->dpagemap.ops = &xe_drm_pagemap_ops;
+
 	if (IS_ERR(addr)) {
 		devm_release_mem_region(dev, res->start, resource_size(res));
 		ret = PTR_ERR(addr);