1 files changed, 96 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_vram_helper_common.c b/drivers/gpu/drm/drm_vram_helper_common.c
new file mode 100644
index 000000000000..e9c9f9a80ba3
--- /dev/null
+++ b/drivers/gpu/drm/drm_vram_helper_common.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/module.h>
+
+/**
+ * DOC: overview
+ *
+ * This library provides &struct drm_gem_vram_object (GEM VRAM), a GEM
+ * buffer object that is backed by video RAM. It can be used for
+ * framebuffer devices with dedicated memory. The video RAM can be
+ * managed with &struct drm_vram_mm (VRAM MM). Both data structures are
+ * supposed to be used together, but can also be used individually.
+ *
+ * With the GEM interface userspace applications create, manage and destroy
+ * graphics buffers, such as an on-screen framebuffer. GEM does not provide
+ * an implementation of these interfaces. It's up to the DRM driver to
+ * provide an implementation that suits the hardware. If the hardware device
+ * contains dedicated video memory, the DRM driver can use the VRAM helper
+ * library. Each active buffer object is stored in video RAM. Active
+ * buffer are used for drawing the current frame, typically something like
+ * the frame's scanout buffer or the cursor image. If there's no more space
+ * left in VRAM, inactive GEM objects can be moved to system memory.
+ *
+ * The easiest way to use the VRAM helper library is to call
+ * drm_vram_helper_alloc_mm(). The function allocates and initializes an
+ * instance of &struct drm_vram_mm in &struct drm_device.vram_mm . Use
+ * &DRM_GEM_VRAM_DRIVER to initialize &struct drm_driver and
+ * &DRM_VRAM_MM_FILE_OPERATIONS to initialize &struct file_operations;
+ * as illustrated below.
+ *
+ * .. code-block:: c
+ *
+ *	struct file_operations fops ={
+ *		.owner = THIS_MODULE,
+ *		DRM_VRAM_MM_FILE_OPERATION
+ *	};
+ *	struct drm_driver drv = {
+ *		.driver_feature = DRM_ ... ,
+ *		.fops = &fops,
+ *		DRM_GEM_VRAM_DRIVER
+ *	};
+ *
+ *	int init_drm_driver()
+ *	{
+ *		struct drm_device *dev;
+ *		uint64_t vram_base;
+ *		unsigned long vram_size;
+ *		int ret;
+ *
+ *		// setup device, vram base and size
+ *		// ...
+ *
+ *		ret = drm_vram_helper_alloc_mm(dev, vram_base, vram_size,
+ *					       &drm_gem_vram_mm_funcs);
+ *		if (ret)
+ *			return ret;
+ *		return 0;
+ *	}
+ *
+ * This creates an instance of &struct drm_vram_mm, exports DRM userspace
+ * interfaces for GEM buffer management and initializes file operations to
+ * allow for accessing created GEM buffers. With this setup, the DRM driver
+ * manages an area of video RAM with VRAM MM and provides GEM VRAM objects
+ * to userspace.
+ *
+ * To clean up the VRAM memory management, call drm_vram_helper_release_mm()
+ * in the driver's clean-up code.
+ *
+ * .. code-block:: c
+ *
+ *	void fini_drm_driver()
+ *	{
+ *		struct drm_device *dev = ...;
+ *
+ *		drm_vram_helper_release_mm(dev);
+ *	}
+ *
+ * For drawing or scanout operations, buffer object have to be pinned in video
+ * RAM. Call drm_gem_vram_pin() with &DRM_GEM_VRAM_PL_FLAG_VRAM or
+ * &DRM_GEM_VRAM_PL_FLAG_SYSTEM to pin a buffer object in video RAM or system
+ * memory. Call drm_gem_vram_unpin() to release the pinned object afterwards.
+ *
+ * A buffer object that is pinned in video RAM has a fixed address within that
+ * memory region. Call drm_gem_vram_offset() to retrieve this value. Typically
+ * it's used to program the hardware's scanout engine for framebuffers, set
+ * the cursor overlay's image for a mouse cursor, or use it as input to the
+ * hardware's draing engine.
+ *
+ * To access a buffer object's memory from the DRM driver, call
+ * drm_gem_vram_kmap(). It (optionally) maps the buffer into kernel address
+ * space and returns the memory address. Use drm_gem_vram_kunmap() to
+ * release the mapping.
+ */
+
+MODULE_DESCRIPTION("DRM VRAM memory-management helpers");
+MODULE_LICENSE("GPL");