Re: [PATCH 2/5] drm/prime: make the pages array optional for drm_prime_sg_to_page_addr_arrays

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Feb 27, 2018 at 12:49:57PM +0100, Christian König wrote:
> Most of the time we only need the dma addresses.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/gpu/drm/drm_prime.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index c38dacda6119..7856a9b3f8a8 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -922,40 +922,40 @@ EXPORT_SYMBOL(drm_prime_pages_to_sg);
>  /**
>   * drm_prime_sg_to_page_addr_arrays - convert an sg table into a page array
>   * @sgt: scatter-gather table to convert
> - * @pages: array of page pointers to store the page array in
> + * @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_pages: size of both the passed-in arrays
> + * @max_entries: size of both the passed-in arrays
>   *
>   * 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.
>   */

Can't we just teach ttm to use sgts wherever needed, and deprecate
exporting dma-bufs to page arrays (which really breaks the abstraction
entirely and was just a quick hack to get things going that stuck around
for years). Last time I looked into ttm the only thing it did is convert
it back to sgts again (after calling dma_map once more, which the exporter
should have done already for you).
-Daniel

>  int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
> -				     dma_addr_t *addrs, int max_pages)
> +				     dma_addr_t *addrs, int max_entries)
>  {
>  	unsigned count;
>  	struct scatterlist *sg;
>  	struct page *page;
> -	u32 len;
> -	int pg_index;
> +	u32 len, index;
>  	dma_addr_t addr;
>  
> -	pg_index = 0;
> +	index = 0;
>  	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
>  		len = sg->length;
>  		page = sg_page(sg);
>  		addr = sg_dma_address(sg);
>  
>  		while (len > 0) {
> -			if (WARN_ON(pg_index >= max_pages))
> +			if (WARN_ON(index >= max_entries))
>  				return -1;
> -			pages[pg_index] = page;
> +			if (pages)
> +				pages[index] = page;
>  			if (addrs)
> -				addrs[pg_index] = addr;
> +				addrs[index] = addr;
>  
>  			page++;
>  			addr += PAGE_SIZE;
>  			len -= PAGE_SIZE;
> -			pg_index++;
> +			index++;
>  		}
>  	}
>  	return 0;
> -- 
> 2.14.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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