linux-kernel - Re: [PATCH 1/3] drm: add gem ttm helpers

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Date:   Tue, 6 Aug 2019 15:54:26 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, tzimmermann@...e.de,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] drm: add gem ttm helpers

On Tue, Aug 06, 2019 at 03:34:52PM +0200, Gerd Hoffmann wrote:
> Now with ttm_buffer_object being a subclass of drm_gem_object we can
> easily lookup ttm_buffer_object for a given drm_gem_object, which in
> turm allows to create common helper functions.  This patch starts off
> with dump mmap helpers.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>  include/drm/drm_gem_ttm_helper.h     | 27 +++++++++++++++
>  drivers/gpu/drm/drm_gem_ttm_helper.c | 52 ++++++++++++++++++++++++++++
>  drivers/gpu/drm/Kconfig              |  7 ++++
>  drivers/gpu/drm/Makefile             |  3 ++
>  4 files changed, 89 insertions(+)
>  create mode 100644 include/drm/drm_gem_ttm_helper.h
>  create mode 100644 drivers/gpu/drm/drm_gem_ttm_helper.c
> 
> diff --git a/include/drm/drm_gem_ttm_helper.h b/include/drm/drm_gem_ttm_helper.h
> new file mode 100644
> index 000000000000..2c6874190b17
> --- /dev/null
> +++ b/include/drm/drm_gem_ttm_helper.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#ifndef DRM_GEM_TTM_HELPER_H
> +#define DRM_GEM_TTM_HELPER_H
> +
> +#include <drm/drm_gem.h>
> +#include <drm/ttm/ttm_bo_api.h>
> +#include <linux/kernel.h> /* for container_of() */
> +
> +/**
> + * Returns the container of type &struct ttm_buffer_object
> + * for field base.
> + * @gem:	the GEM object
> + * Returns:	The containing GEM VRAM object
> + */
> +static inline struct ttm_buffer_object *drm_gem_ttm_of_gem(
> +	struct drm_gem_object *gem)
> +{
> +	return container_of(gem, struct ttm_buffer_object, base);
> +}
> +
> +u64 drm_gem_ttm_mmap_offset(struct ttm_buffer_object *bo);
> +int drm_gem_ttm_driver_dumb_mmap_offset(struct drm_file *file,
> +					struct drm_device *dev,
> +					uint32_t handle, uint64_t *offset);
> +
> +#endif
> diff --git a/drivers/gpu/drm/drm_gem_ttm_helper.c b/drivers/gpu/drm/drm_gem_ttm_helper.c
> new file mode 100644
> index 000000000000..b069bd0c4c94
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_gem_ttm_helper.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +#include <drm/drm_gem_ttm_helper.h>
> +
> +/**
> + * drm_gem_ttm_mmap_offset() - Returns a GEM ttm object's mmap offset
> + * @gbo:	the GEM ttm object
> + *
> + * See drm_vma_node_offset_addr() for more information.
> + *
> + * Returns:
> + * The buffer object's offset for userspace mappings on success, or
> + * 0 if no offset is allocated.
> + */
> +u64 drm_gem_ttm_mmap_offset(struct ttm_buffer_object *bo)
> +{
> +	return drm_vma_node_offset_addr(&bo->base.vma_node);

Why do we need a new one here, can't we use the existing gem
implementation for this (there really should only be one I hope, but I
didn't check).

> +}
> +EXPORT_SYMBOL(drm_gem_ttm_mmap_offset);
> +
> +/**
> + * drm_gem_ttm_driver_dumb_mmap_offset() - \
> +	Implements &struct drm_driver.dumb_mmap_offset
> + * @file:	DRM file pointer.
> + * @dev:	DRM device.
> + * @handle:	GEM handle
> + * @offset:	Returns the mapping's memory offset on success
> + *
> + * Returns:
> + * 0 on success, or
> + * a negative errno code otherwise.
> + */
> +int drm_gem_ttm_driver_dumb_mmap_offset(struct drm_file *file,
> +					 struct drm_device *dev,
> +					 uint32_t handle, uint64_t *offset)
> +{
> +	struct drm_gem_object *gem;
> +	struct ttm_buffer_object *bo;
> +
> +	gem = drm_gem_object_lookup(file, handle);
> +	if (!gem)
> +		return -ENOENT;
> +
> +	bo = drm_gem_ttm_of_gem(gem);
> +	*offset = drm_gem_ttm_mmap_offset(bo);
> +
> +	drm_gem_object_put_unlocked(gem);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_gem_ttm_driver_dumb_mmap_offset);

Same for this, you're just upcasting to ttm_bo and then downcasting to
gem_bo again ... I think just a series to roll out the existing gem
helpers everywhere should work?
-Daniel

> +
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index e6f40fb54c9a..f7b25519f95c 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -172,6 +172,13 @@ config DRM_VRAM_HELPER
>  	help
>  	  Helpers for VRAM memory management
>  
> +config DRM_TTM_HELPER
> +	tristate
> +	depends on DRM
> +	select DRM_TTM
> +	help
> +	  Helpers for ttm-based gem objects
> +
>  config DRM_GEM_CMA_HELPER
>  	bool
>  	depends on DRM
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 10f8329a8b71..545c61d6528b 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -37,6 +37,9 @@ drm_vram_helper-y := drm_gem_vram_helper.o \
>  		     drm_vram_mm_helper.o
>  obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o
>  
> +drm_ttm_helper-y := drm_gem_ttm_helper.o
> +obj-$(CONFIG_DRM_TTM_HELPER) += drm_ttm_helper.o
> +
>  drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_dsc.o drm_probe_helper.o \
>  		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
>  		drm_kms_helper_common.o drm_dp_dual_mode_helper.o \
> -- 
> 2.18.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch