linux-kernel - Re: [PATCH v7 02/36] drm: prime: use sgtable iterators in drm_prime_sg_to_page_addr

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Date:   Tue, 7 Jul 2020 16:41:37 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 02/36] drm: prime: use sgtable iterators in
 drm_prime_sg_to_page_addr_arrays()


On 19.06.2020 12:36, Marek Szyprowski wrote:
> Replace the current hand-crafted code for extracting pages and DMA
> addresses from the given scatterlist by the much more robust
> code based on the generic scatterlist iterators and recently
> introduced sg_table-based wrappers. The resulting code is simple and
> easy to understand, so the comment describing the old code is no
> longer needed.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>


Nice simplification.

Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>

Btw, I've wrongly re-configured my e-mail client, so my R-Bs for other 
patches are little bit broken, I will resend them :)


Regards
Andrzej


> ---
>   drivers/gpu/drm/drm_prime.c | 49 ++++++++++++-------------------------
>   1 file changed, 15 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 226cd6ad3985..b717e52e909e 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -990,45 +990,26 @@ EXPORT_SYMBOL(drm_gem_prime_import);
>   int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
>   				     dma_addr_t *addrs, 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
> -	 * 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).
> -	 */
> -	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) {
> -			if (WARN_ON(page_index >= max_entries))
> +	struct sg_dma_page_iter dma_iter;
> +	struct sg_page_iter page_iter;
> +	struct page **p = pages;
> +	dma_addr_t *a = addrs;
> +
> +	if (pages) {
> +		for_each_sgtable_page(sgt, &page_iter, 0) {
> +			if (p - pages >= max_entries)
>   				return -1;
> -			pages[page_index] = page;
> -			page++;
> -			page_len -= PAGE_SIZE;
> -			page_index++;
> +			*p++ = sg_page_iter_page(&page_iter);
>   		}
> -		while (addrs && dma_len > 0) {
> -			if (WARN_ON(dma_index >= max_entries))
> +	}
> +	if (addrs) {
> +		for_each_sgtable_dma_page(sgt, &dma_iter, 0) {
> +			if (a - addrs >= max_entries)
>   				return -1;
> -			addrs[dma_index] = addr;
> -			addr += PAGE_SIZE;
> -			dma_len -= PAGE_SIZE;
> -			dma_index++;
> +			*a++ = sg_page_iter_dma_address(&dma_iter);
>   		}
>   	}
> +
>   	return 0;
>   }
>   EXPORT_SYMBOL(drm_prime_sg_to_page_addr_arrays);