drm/pagemap: Add DRM pagemap

Introduce drm_pagemap ops to map and unmap dma to VRAM resources. In the
local memory case it's a matter of merely providing an offset into the
device's physical address. For future p2p the map and unmap functions may
encode as needed.

Similar to how dma-buf works, let the memory provider (drm_pagemap) provide
the mapping functionality.

v3:
 - Move to drm level include
v4:
 - Fix kernel doc (G.G.)
v5:
 - s/map_dma/device_map (Thomas)
 - s/unmap_dma/device_unmap (Thomas)
v7:
 - Fix kernel doc (CI, Auld)
 - Drop P2P define (Thomas)

Signed-off-by: Matthew Brost <[email protected]>
Signed-off-by: Thomas Hellström <[email protected]>
Reviewed-by: Matthew Brost <[email protected]>
Reviewed-by: Gwan-gyeong Mun <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Thomas Hellström

include/drm/drm_pagemap.h

@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: MIT */
+#ifndef _DRM_PAGEMAP_H_
+#define _DRM_PAGEMAP_H_
+
+#include <linux/dma-direction.h>
+#include <linux/hmm.h>
+#include <linux/types.h>
+
+struct drm_pagemap;
+struct device;
+
+/**
+ * enum drm_interconnect_protocol - Used to identify an interconnect protocol.
+ *
+ * @DRM_INTERCONNECT_SYSTEM: DMA map is system pages
+ * @DRM_INTERCONNECT_DRIVER: DMA map is driver defined
+ */
+enum drm_interconnect_protocol {
+	DRM_INTERCONNECT_SYSTEM,
+	DRM_INTERCONNECT_DRIVER,
+	/* A driver can add private values beyond DRM_INTERCONNECT_DRIVER */
+};
+
+/**
+ * struct drm_pagemap_device_addr - Device address representation.
+ * @addr: The dma address or driver-defined address for driver private interconnects.
+ * @proto: The interconnect protocol.
+ * @order: The page order of the device mapping. (Size is PAGE_SIZE << order).
+ * @dir: The DMA direction.
+ *
+ * Note: There is room for improvement here. We should be able to pack into
+ * 64 bits.
+ */
+struct drm_pagemap_device_addr {
+	dma_addr_t addr;
+	u64 proto : 54;
+	u64 order : 8;
+	u64 dir : 2;
+};
+
+/**
+ * drm_pagemap_device_addr_encode() - Encode a dma address with metadata
+ * @addr: The dma address or driver-defined address for driver private interconnects.
+ * @proto: The interconnect protocol.
+ * @order: The page order of the dma mapping. (Size is PAGE_SIZE << order).
+ * @dir: The DMA direction.
+ *
+ * Return: A struct drm_pagemap_device_addr encoding the above information.
+ */
+static inline struct drm_pagemap_device_addr
+drm_pagemap_device_addr_encode(dma_addr_t addr,
+			       enum drm_interconnect_protocol proto,
+			       unsigned int order,
+			       enum dma_data_direction dir)
+{
+	return (struct drm_pagemap_device_addr) {
+		.addr = addr,
+		.proto = proto,
+		.order = order,
+		.dir = dir,
+	};
+}
+
+/**
+ * struct drm_pagemap_ops: Ops for a drm-pagemap.
+ */
+struct drm_pagemap_ops {
+	/**
+	 * @device_map: Map for device access or provide a virtual address suitable for
+	 *
+	 * @dpagemap: The struct drm_pagemap for the page.
+	 * @dev: The device mapper.
+	 * @page: The page to map.
+	 * @order: The page order of the device mapping. (Size is PAGE_SIZE << order).
+	 * @dir: The transfer direction.
+	 */
+	struct drm_pagemap_device_addr (*device_map)(struct drm_pagemap *dpagemap,
+						     struct device *dev,
+						     struct page *page,
+						     unsigned int order,
+						     enum dma_data_direction dir);
+
+	/**
+	 * @device_unmap: Unmap a device address previously obtained using @device_map.
+	 *
+	 * @dpagemap: The struct drm_pagemap for the mapping.
+	 * @dev: The device unmapper.
+	 * @addr: The device address obtained when mapping.
+	 */
+	void (*device_unmap)(struct drm_pagemap *dpagemap,
+			     struct device *dev,
+			     struct drm_pagemap_device_addr addr);
+
+};
+
+/**
+ * struct drm_pagemap: Additional information for a struct dev_pagemap
+ * used for device p2p handshaking.
+ * @ops: The struct drm_pagemap_ops.
+ * @dev: The struct drevice owning the device-private memory.
+ */
+struct drm_pagemap {
+	const struct drm_pagemap_ops *ops;
+	struct device *dev;
+};
+
+#endif