[PATCH 4/5] drm/ttm: add ttm_sg_tt_init

[Christian König]

Hi guys,

at least on amdgpu and radeon the page array allocated by 
ttm_dma_tt_init is completely unused in the case of DMA-buf sharing. So 
I'm trying to get rid of that by only allocating the DMA address array.

Now the only other user of DMA-buf together with ttm_dma_tt_init is 
Nouveau. So my question is are you guys using the page array anywhere in 
your kernel driver in case of a DMA-buf sharing?

If no then I could just make this the default behavior for all drivers 
and save quite a bit of memory for everybody.

Thanks,
Christian.

Am 27.02.2018 um 12:49 schrieb Christian König:
> This allows drivers to only allocate dma addresses, but not a page
> array.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/gpu/drm/ttm/ttm_tt.c | 54 ++++++++++++++++++++++++++++++++++++--------
>   include/drm/ttm/ttm_tt.h     |  2 ++
>   2 files changed, 47 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index 8e0b525cda00..971133106ec2 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -108,6 +108,16 @@ static int ttm_dma_tt_alloc_page_directory(struct ttm_dma_tt *ttm)
>   	return 0;
>   }
>   
> +static int ttm_sg_tt_alloc_page_directory(struct ttm_dma_tt *ttm)
> +{
> +	ttm->dma_address = kvmalloc_array(ttm->ttm.num_pages,
> +					  sizeof(*ttm->dma_address),
> +					  GFP_KERNEL | __GFP_ZERO);
> +	if (!ttm->dma_address)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
>   #ifdef CONFIG_X86
>   static inline int ttm_tt_set_page_caching(struct page *p,
>   					  enum ttm_caching_state c_old,
> @@ -227,8 +237,8 @@ void ttm_tt_destroy(struct ttm_tt *ttm)
>   	ttm->func->destroy(ttm);
>   }
>   
> -int ttm_tt_init(struct ttm_tt *ttm, struct ttm_bo_device *bdev,
> -		unsigned long size, uint32_t page_flags)
> +void ttm_tt_init_fields(struct ttm_tt *ttm, struct ttm_bo_device *bdev,
> +			unsigned long size, uint32_t page_flags)
>   {
>   	ttm->bdev = bdev;
>   	ttm->num_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> @@ -236,6 +246,12 @@ int ttm_tt_init(struct ttm_tt *ttm, struct ttm_bo_device *bdev,
>   	ttm->page_flags = page_flags;
>   	ttm->state = tt_unpopulated;
>   	ttm->swap_storage = NULL;
> +}
> +
> +int ttm_tt_init(struct ttm_tt *ttm, struct ttm_bo_device *bdev,
> +		unsigned long size, uint32_t page_flags)
> +{
> +	ttm_tt_init_fields(ttm, bdev, size, page_flags);
>   
>   	if (ttm_tt_alloc_page_directory(ttm)) {
>   		ttm_tt_destroy(ttm);
> @@ -258,12 +274,7 @@ int ttm_dma_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
>   {
>   	struct ttm_tt *ttm = &ttm_dma->ttm;
>   
> -	ttm->bdev = bdev;
> -	ttm->num_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> -	ttm->caching_state = tt_cached;
> -	ttm->page_flags = page_flags;
> -	ttm->state = tt_unpopulated;
> -	ttm->swap_storage = NULL;
> +	ttm_tt_init_fields(ttm, bdev, size, page_flags);
>   
>   	INIT_LIST_HEAD(&ttm_dma->pages_list);
>   	if (ttm_dma_tt_alloc_page_directory(ttm_dma)) {
> @@ -275,11 +286,36 @@ int ttm_dma_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
>   }
>   EXPORT_SYMBOL(ttm_dma_tt_init);
>   
> +int ttm_sg_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
> +		   unsigned long size, uint32_t page_flags)
> +{
> +	struct ttm_tt *ttm = &ttm_dma->ttm;
> +	int ret;
> +
> +	ttm_tt_init_fields(ttm, bdev, size, page_flags);
> +
> +	INIT_LIST_HEAD(&ttm_dma->pages_list);
> +	if (page_flags & TTM_PAGE_FLAG_SG)
> +		ret = ttm_sg_tt_alloc_page_directory(ttm_dma);
> +	else
> +		ret = ttm_dma_tt_alloc_page_directory(ttm_dma);
> +	if (ret) {
> +		ttm_tt_destroy(ttm);
> +		pr_err("Failed allocating page table\n");
> +		return -ENOMEM;
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL(ttm_sg_tt_init);
> +
>   void ttm_dma_tt_fini(struct ttm_dma_tt *ttm_dma)
>   {
>   	struct ttm_tt *ttm = &ttm_dma->ttm;
>   
> -	kvfree(ttm->pages);
> +	if (ttm->pages)
> +		kvfree(ttm->pages);
> +	else
> +		kvfree(ttm_dma->dma_address);
>   	ttm->pages = NULL;
>   	ttm_dma->dma_address = NULL;
>   }
> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
> index 9c78556b488e..1cf316a4257c 100644
> --- a/include/drm/ttm/ttm_tt.h
> +++ b/include/drm/ttm/ttm_tt.h
> @@ -163,6 +163,8 @@ int ttm_tt_init(struct ttm_tt *ttm, struct ttm_bo_device *bdev,
>   		unsigned long size, uint32_t page_flags);
>   int ttm_dma_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
>   		    unsigned long size, uint32_t page_flags);
> +int ttm_sg_tt_init(struct ttm_dma_tt *ttm_dma, struct ttm_bo_device *bdev,
> +		   unsigned long size, uint32_t page_flags);
>   
>   /**
>    * ttm_tt_fini