Date:   Fri, 9 Oct 2020 18:24:44 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Christian König 
        <ckoenig.leichtzumerken@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, dri-devel@...ts.freedesktop.org,
        linux-media@...r.kernel.org, chris@...is-wilson.co.uk,
        airlied@...hat.com, akpm@...ux-foundation.org, daniel@...ll.ch,
        sumit.semwal@...aro.org, willy@...radead.org, jhubbard@...dia.com,
        jgg@...pe.ca
Subject: Re: [PATCH 6/6] drm/prime: document that use the page array is
 deprecated v2

On Fri, Oct 09, 2020 at 05:03:42PM +0200, Christian König wrote:
> We have reoccurring requests on this so better document that
> this approach doesn't work and dma_buf_mmap() needs to be used instead.
> 
> v2: split it into two functions
> 
> Signed-off-by: Christian König <christian.koenig@....com>

Patches 3-5:

Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>

This one looks good, but you have it on a strange baseline. This doesn't
contain the sg walking fixes from Marek, so reintroduces the bugs.
Probably need to request a backmerge chain, first of -rc8 into drm-next,
and then that into drm-misc-next.

Everything else in here lgtm.
-Daniel



> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     |  9 ++-
>  drivers/gpu/drm/drm_prime.c                 | 67 +++++++++++++++------
>  drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c |  3 +-
>  drivers/gpu/drm/msm/msm_gem.c               |  2 +-
>  drivers/gpu/drm/nouveau/nouveau_bo.c        |  5 +-
>  drivers/gpu/drm/radeon/radeon_ttm.c         |  9 ++-
>  drivers/gpu/drm/vgem/vgem_drv.c             |  3 +-
>  drivers/gpu/drm/vkms/vkms_gem.c             |  2 +-
>  drivers/gpu/drm/xen/xen_drm_front_gem.c     |  4 +-
>  include/drm/drm_prime.h                     |  7 ++-
>  10 files changed, 69 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index ac463e706b19..6a65490de391 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1011,8 +1011,8 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_bo_device *bdev,
>  		goto release_sg;
>  
>  	/* convert SG to linear array of pages and dma addresses */
> -	drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL, gtt->ttm.dma_address,
> -					 ttm->num_pages);
> +	drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
> +				       ttm->num_pages);
>  
>  	return 0;
>  
> @@ -1345,9 +1345,8 @@ static int amdgpu_ttm_tt_populate(struct ttm_bo_device *bdev,
>  			ttm->sg = sgt;
>  		}
>  
> -		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
> -						 gtt->ttm.dma_address,
> -						 ttm->num_pages);
> +		drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
> +					       ttm->num_pages);
>  		ttm_tt_set_populated(ttm);
>  		return 0;
>  	}
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 4910c446db83..8b750c074494 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -954,27 +954,25 @@ struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
>  EXPORT_SYMBOL(drm_gem_prime_import);
>  
>  /**
> - * drm_prime_sg_to_page_addr_arrays - convert an sg table into a page array
> + * drm_prime_sg_to_page_array - convert an sg table into a page array
>   * @sgt: scatter-gather table to convert
> - * @pages: optional array of page pointers to store the page array in
> - * @addrs: optional array to store the dma bus address of each page
> - * @max_entries: size of both the passed-in arrays
> + * @pages: array of page pointers to store the pages in
> + * @max_entries: size of the passed-in array
>   *
> - * Exports an sg table into an array of pages and addresses. This is currently
> - * required by the TTM driver in order to do correct fault handling.
> + * Exports an sg table into an array of pages.
>   *
> - * Drivers can use this in their &drm_driver.gem_prime_import_sg_table
> - * implementation.
> + * This function is deprecated and strongly discouraged to be used.
> + * The page array is only useful for page faults and those can corrupt fields
> + * in the struct page if they are not handled by the exporting driver.
>   */
> -int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
> -				     dma_addr_t *addrs, int max_entries)
> +int __deprecated drm_prime_sg_to_page_array(struct sg_table *sgt,
> +					    struct page **pages,
> +					    int max_entries)
>  {
>  	unsigned count;
>  	struct scatterlist *sg;
>  	struct page *page;
>  	u32 page_len, page_index;
> -	dma_addr_t addr;
> -	u32 dma_len, dma_index;
>  
>  	/*
>  	 * Scatterlist elements contains both pages and DMA addresses, but
> @@ -984,14 +982,11 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
>  	 * described by the sg_dma_address(sg).
>  	 */
>  	page_index = 0;
> -	dma_index = 0;
>  	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
>  		page_len = sg->length;
>  		page = sg_page(sg);
> -		dma_len = sg_dma_len(sg);
> -		addr = sg_dma_address(sg);
>  
> -		while (pages && page_len > 0) {
> +		while (page_len > 0) {
>  			if (WARN_ON(page_index >= max_entries))
>  				return -1;
>  			pages[page_index] = page;
> @@ -999,7 +994,43 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
>  			page_len -= PAGE_SIZE;
>  			page_index++;
>  		}
> -		while (addrs && dma_len > 0) {
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_prime_sg_to_page_array);
> +
> +/**
> + * drm_prime_sg_to_dma_addr_array - convert an sg table into a dma addr array
> + * @sgt: scatter-gather table to convert
> + * @addrs: array to store the dma bus address of each page
> + * @max_entries: size of both the passed-in arrays
> + *
> + * Exports an sg table into an array of addresses.
> + *
> + * Drivers should use this in their &drm_driver.gem_prime_import_sg_table

s/should/can/

There's no requirement, if your driver just handles everything as an sgt
there's no conversion needed.

> + * implementation.
> + */
> +int drm_prime_sg_to_dma_addr_array(struct sg_table *sgt, dma_addr_t *addrs,
> +				   int max_entries)
> +{
> +	struct scatterlist *sg;
> +	u32 dma_len, dma_index;
> +	dma_addr_t addr;
> +	unsigned count;
> +
> +	/*
> +	 * Scatterlist elements contains both pages and DMA addresses, but
> +	 * one shoud not assume 1:1 relation between them. The sg->length is
> +	 * the size of the physical memory chunk described by the sg->page,
> +	 * while sg_dma_len(sg) is the size of the DMA (IO virtual) chunk
> +	 * described by the sg_dma_address(sg).
> +	 */
> +	dma_index = 0;
> +	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
> +		dma_len = sg_dma_len(sg);
> +		addr = sg_dma_address(sg);
> +
> +		while (dma_len > 0) {
>  			if (WARN_ON(dma_index >= max_entries))
>  				return -1;
>  			addrs[dma_index] = addr;
> @@ -1010,7 +1041,7 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
>  	}
>  	return 0;
>  }
> -EXPORT_SYMBOL(drm_prime_sg_to_page_addr_arrays);
> +EXPORT_SYMBOL(drm_prime_sg_to_dma_addr_array);
>  
>  /**
>   * drm_prime_gem_destroy - helper to clean up a PRIME-imported GEM object
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> index 135fbff6fecf..8c04b8e8054c 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c
> @@ -133,8 +133,7 @@ struct drm_gem_object *etnaviv_gem_prime_import_sg_table(struct drm_device *dev,
>  		goto fail;
>  	}
>  
> -	ret = drm_prime_sg_to_page_addr_arrays(sgt, etnaviv_obj->pages,
> -					       NULL, npages);
> +	ret = drm_prime_sg_to_page_array(sgt, etnaviv_obj->pages, npages);
>  	if (ret)
>  		goto fail;
>  
> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> index a71f42870d5e..616b87641740 100644
> --- a/drivers/gpu/drm/msm/msm_gem.c
> +++ b/drivers/gpu/drm/msm/msm_gem.c
> @@ -1174,7 +1174,7 @@ struct drm_gem_object *msm_gem_import(struct drm_device *dev,
>  		goto fail;
>  	}
>  
> -	ret = drm_prime_sg_to_page_addr_arrays(sgt, msm_obj->pages, NULL, npages);
> +	ret = drm_prime_sg_to_page_array(sgt, msm_obj->pages, npages);
>  	if (ret) {
>  		mutex_unlock(&msm_obj->lock);
>  		goto fail;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index e378bb491688..835edd74ef59 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -1299,9 +1299,8 @@ nouveau_ttm_tt_populate(struct ttm_bo_device *bdev,
>  		return 0;
>  
>  	if (slave && ttm->sg) {
> -		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
> -						 ttm_dma->dma_address,
> -						 ttm->num_pages);
> +		drm_prime_sg_to_dma_addr_array(ttm->sg, ttm_dma->dma_address,
> +					       ttm->num_pages);
>  		ttm_tt_set_populated(ttm);
>  		return 0;
>  	}
> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index 4b92cdbcd29b..7997e4564576 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -474,8 +474,8 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_bo_device *bdev, struct ttm_tt *
>  	if (r)
>  		goto release_sg;
>  
> -	drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL, gtt->ttm.dma_address,
> -					 ttm->num_pages);
> +	drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
> +				       ttm->num_pages);
>  
>  	return 0;
>  
> @@ -642,9 +642,8 @@ static int radeon_ttm_tt_populate(struct ttm_bo_device *bdev,
>  	}
>  
>  	if (slave && ttm->sg) {
> -		drm_prime_sg_to_page_addr_arrays(ttm->sg, NULL,
> -						 gtt->ttm.dma_address,
> -						 ttm->num_pages);
> +		drm_prime_sg_to_dma_addr_array(ttm->sg, gtt->ttm.dma_address,
> +					       ttm->num_pages);
>  		ttm_tt_set_populated(ttm);
>  		return 0;
>  	}
> diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> index ea0eecae5153..e505e5a291b3 100644
> --- a/drivers/gpu/drm/vgem/vgem_drv.c
> +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> @@ -356,8 +356,7 @@ static struct drm_gem_object *vgem_prime_import_sg_table(struct drm_device *dev,
>  	}
>  
>  	obj->pages_pin_count++; /* perma-pinned */
> -	drm_prime_sg_to_page_addr_arrays(obj->table, obj->pages, NULL,
> -					npages);
> +	drm_prime_sg_to_page_array(obj->table, obj->pages, npages);
>  	return &obj->base;
>  }
>  
> diff --git a/drivers/gpu/drm/vkms/vkms_gem.c b/drivers/gpu/drm/vkms/vkms_gem.c
> index 19a0e260a4df..a2ff21f47101 100644
> --- a/drivers/gpu/drm/vkms/vkms_gem.c
> +++ b/drivers/gpu/drm/vkms/vkms_gem.c
> @@ -256,6 +256,6 @@ vkms_prime_import_sg_table(struct drm_device *dev,
>  		return ERR_PTR(-ENOMEM);
>  	}
>  
> -	drm_prime_sg_to_page_addr_arrays(sg, obj->pages, NULL, npages);
> +	drm_prime_sg_to_page_array(sg, obj->pages, npages);
>  	return &obj->gem;
>  }
> diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c
> index f3830a0d1808..f4150ddfc5e2 100644
> --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
> +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
> @@ -220,8 +220,8 @@ xen_drm_front_gem_import_sg_table(struct drm_device *dev,
>  
>  	xen_obj->sgt_imported = sgt;
>  
> -	ret = drm_prime_sg_to_page_addr_arrays(sgt, xen_obj->pages,
> -					       NULL, xen_obj->num_pages);
> +	ret = drm_prime_sg_to_page_array(sgt, xen_obj->pages,
> +					 xen_obj->num_pages);
>  	if (ret < 0)
>  		return ERR_PTR(ret);
>  
> diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
> index 093f760cc131..4bda9ab3a3bb 100644
> --- a/include/drm/drm_prime.h
> +++ b/include/drm/drm_prime.h
> @@ -103,8 +103,9 @@ struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
>  
>  void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg);
>  
> -int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
> -				     dma_addr_t *addrs, int max_pages);
> -
> +int drm_prime_sg_to_page_array(struct sg_table *sgt, struct page **pages,
> +			       int max_pages);
> +int drm_prime_sg_to_dma_addr_array(struct sg_table *sgt, dma_addr_t *addrs,
> +				   int max_pages);
>  
>  #endif /* __DRM_PRIME_H__ */
> -- 
> 2.17.1
> 

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

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