Commit 5fbc2c2b authored by Imre Deak's avatar Imre Deak
Browse files

drm/i915/gem: Add a helper to read data from a GEM object page 



Add a simple helper to read data with the CPU from the page of a GEM
object. Do the read either via a kmap if the object has struct pages
or an iomap otherwise. This is needed by the next patch, reading a u64
value from the object (w/o requiring the obj to be mapped to the GPU).

Suggested by Chris.

v2 (Chris):
- Sanitize the type and order of func params.
- Avoid consts requiring too many casts.
- Use BUG_ON instead of WARN_ON, simplify the conditions.
- Fix __iomem sparse errors.
- Leave locking/syncing/pinning up to the caller, require only that the
  caller has pinned the object pages.
- Check for iomem backing store before reading via an iomap.
v3:
- Fix offset passed to io_mapping_map_wc() missing a mem.region.start
  delta. (Chris, Matthew)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Signed-off-by: default avatarImre Deak <imre.deak@intel.com>
Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20210120213834.1435710-1-imre.deak@intel.com
parent 87199e4c

drivers/gpu/drm/i915/gem/i915_gem_object.c

+65 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 
#include "i915_gem_mman.h"

#include "i915_gem_object.h"

#include "i915_globals.h"

#include "i915_memcpy.h"

#include "i915_trace.h"



static struct i915_global_object {
@@ -383,6 +384,70 @@ void __i915_gem_object_invalidate_frontbuffer(struct drm_i915_gem_object *obj, 
	}

}



static void

i915_gem_object_read_from_page_kmap(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)

{

	void *src_map;

	void *src_ptr;



	src_map = kmap_atomic(i915_gem_object_get_page(obj, offset >> PAGE_SHIFT));



	src_ptr = src_map + offset_in_page(offset);

	if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ))

		drm_clflush_virt_range(src_ptr, size);

	memcpy(dst, src_ptr, size);



	kunmap_atomic(src_map);

}



static void

i915_gem_object_read_from_page_iomap(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)

{

	void __iomem *src_map;

	void __iomem *src_ptr;

	dma_addr_t dma = i915_gem_object_get_dma_address(obj, offset >> PAGE_SHIFT);



	src_map = io_mapping_map_wc(&obj->mm.region->iomap,

				    dma - obj->mm.region->region.start,

				    PAGE_SIZE);



	src_ptr = src_map + offset_in_page(offset);

	if (!i915_memcpy_from_wc(dst, (void __force *)src_ptr, size))

		memcpy_fromio(dst, src_ptr, size);



	io_mapping_unmap(src_map);

}



/**

 * i915_gem_object_read_from_page - read data from the page of a GEM object

 * @obj: GEM object to read from

 * @offset: offset within the object

 * @dst: buffer to store the read data

 * @size: size to read

 *

 * Reads data from @obj at the specified offset. The requested region to read

 * from can't cross a page boundary. The caller must ensure that @obj pages

 * are pinned and that @obj is synced wrt. any related writes.

 *

 * Returns 0 on success or -ENODEV if the type of @obj's backing store is

 * unsupported.

 */

int i915_gem_object_read_from_page(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size)

{

	GEM_BUG_ON(offset >= obj->base.size);

	GEM_BUG_ON(offset_in_page(offset) > PAGE_SIZE - size);

	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));



	if (i915_gem_object_has_struct_page(obj))

		i915_gem_object_read_from_page_kmap(obj, offset, dst, size);

	else if (i915_gem_object_has_iomem(obj))

		i915_gem_object_read_from_page_iomap(obj, offset, dst, size);

	else

		return -ENODEV;



	return 0;

}



void i915_gem_init__objects(struct drm_i915_private *i915)

{

	INIT_WORK(&i915->mm.free_work, __i915_gem_free_work);

drivers/gpu/drm/i915/gem/i915_gem_object.h

+8 −0
Original line number Diff line number Diff line
@@ -200,6 +200,12 @@ i915_gem_object_has_struct_page(const struct drm_i915_gem_object *obj) 
	return i915_gem_object_type_has(obj, I915_GEM_OBJECT_HAS_STRUCT_PAGE);

}



static inline bool

i915_gem_object_has_iomem(const struct drm_i915_gem_object *obj)

{

	return i915_gem_object_type_has(obj, I915_GEM_OBJECT_HAS_IOMEM);

}



static inline bool

i915_gem_object_is_shrinkable(const struct drm_i915_gem_object *obj)

{
@@ -540,4 +546,6 @@ i915_gem_object_invalidate_frontbuffer(struct drm_i915_gem_object *obj, 
		__i915_gem_object_invalidate_frontbuffer(obj, origin);

}



int i915_gem_object_read_from_page(struct drm_i915_gem_object *obj, u64 offset, void *dst, int size);



#endif