[PATCH 4/8] drm/xe: Introduce a helper to get dpa from pfn

[Oak Zeng <oak.zeng@intel.com>]

Since we now create struct page backing for each vram page,
each vram page now also has a pfn, just like system memory.
This allow us to calcuate device physical address from pfn.

v1: move the function to xe_svm.h (Matt)
    s/vram_pfn_to_dpa/xe_mem_region_pfn_to_dpa (Matt)
    add kernel document for the helper (Thomas)

Signed-off-by: Oak Zeng <oak.zeng@intel.com>
---
 drivers/gpu/drm/xe/xe_svm.h | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_svm.h b/drivers/gpu/drm/xe/xe_svm.h
index e944971cfc6d..8a34429eb674 100644
--- a/drivers/gpu/drm/xe/xe_svm.h
+++ b/drivers/gpu/drm/xe/xe_svm.h
@@ -6,8 +6,31 @@
 #ifndef __XE_SVM_H
 #define __XE_SVM_H
 
-struct xe_tile;
-struct xe_mem_region;
+#include "xe_device_types.h"
+#include "xe_device.h"
+#include "xe_assert.h"
+
+/**
+ * xe_mem_region_pfn_to_dpa() - Calculate page's dpa from pfn
+ *
+ * @mr: The memory region that page resides in
+ * @pfn: page frame number of the page
+ *
+ * Returns: the device physical address of the page
+ */
+static inline u64 xe_mem_region_pfn_to_dpa(struct xe_mem_region *mr, u64 pfn)
+{
+	u64 dpa;
+	struct xe_tile *tile = xe_mem_region_to_tile(mr);
+	struct xe_device *xe = tile_to_xe(tile);
+	u64 offset;
+
+	xe_assert(xe, (pfn << PAGE_SHIFT) >= mr->hpa_base);
+	offset = (pfn << PAGE_SHIFT) - mr->hpa_base;
+	dpa = mr->dpa_base + offset;
+
+	return dpa;
+}
 
 int xe_devm_add(struct xe_tile *tile, struct xe_mem_region *mr);
 void xe_devm_remove(struct xe_tile *tile, struct xe_mem_region *mr);
-- 
2.26.3