Re: [PATCH 6/6] drm/prime: document that use the page array is deprecated v2

From: Daniel Vetter
Date: Fri Oct 09 2020 - 12:24:50 EST

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@xxxxxxx>

Patches 3-5:

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

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