linux-kernel - Re: [PATCH v2 2/3] drm: shmem: Add drm_gem_shmem_map

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Message-ID: <20190516202644.GE3851@phenom.ffwll.local>
Date:   Thu, 16 May 2019 22:26:44 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Steven Price <steven.price@....com>
Cc:     Daniel Vetter <daniel@...ll.ch>, Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        David Airlie <airlied@...ux.ie>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kukjin Kim <kgene@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] drm: shmem: Add drm_gem_shmem_map_offset() wrapper

On Thu, May 16, 2019 at 03:14:46PM +0100, Steven Price wrote:
> Provide a wrapper for drm_gem_map_offset() for clients of shmem. This
> wrapper provides the correct semantics for the drm_gem_shmem_mmap()
> callback.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 20 ++++++++++++++++++++
>  include/drm/drm_gem_shmem_helper.h     |  2 ++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 1ee208c2c85e..9dbebc4897d1 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -400,6 +400,26 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
>  
> +/**
> + * drm_gem_map_offset - return the fake mmap offset for a gem object
> + * @file: drm file-private structure containing the gem object
> + * @dev: corresponding drm_device
> + * @handle: gem object handle
> + * @offset: return location for the fake mmap offset
> + *
> + * This provides an offset suitable for user space to return to the
> + * drm_gem_shmem_mmap() callback via an mmap() call.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_map_offset(struct drm_file *file, struct drm_device *dev,
> +			     u32 handle, u64 *offset)
> +{
> +	return drm_gem_map_offset(file, dev, handle, offset);
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_map_offset);

Not seeing the point of this mapper, since drm_gem_shmem_map_offset isn't
speficic at all. It works for dumb, shmem, cma and private objects all
equally well. I'd drop this and just directly call the underlying thing,
no need to layer helpers.
-Daniel

> +
>  static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 038b6d313447..4239ddaaaa4f 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -128,6 +128,8 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
>  int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
>  			      struct drm_mode_create_dumb *args);
>  
> +int drm_gem_shmem_map_offset(struct drm_file *file, struct drm_device *dev,
> +			     u32 handle, u64 *offset);
>  int drm_gem_shmem_mmap(struct file *filp, struct vm_area_struct *vma);
>  
>  extern const struct vm_operations_struct drm_gem_shmem_vm_ops;
> -- 
> 2.20.1
> 

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