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Message-ID: <CADnq5_NpHvmRvzvh1aF293UDUXiHF4Dg1rRNkt7XbM_VB98JCg@mail.gmail.com>
Date: Sun, 5 Apr 2020 10:47:49 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Maling list - DRI developers <dri-devel@...ts.freedesktop.org>,
linux-samsung-soc@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
David Airlie <airlied@...ux.ie>,
Shane Francis <bigbeeshane@...il.com>,
"Michael J . Ruhl" <michael.j.ruhl@...el.com>,
"for 3.8" <stable@...r.kernel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH v2] drm/prime: fix extracting of the DMA addresses from a scatterlist
On Fri, Mar 27, 2020 at 12:23 PM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> Scatterlist elements contains both pages and DMA addresses, but one
> should 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).
>
> The proper way of extracting both: pages and DMA addresses of the whole
> buffer described by a scatterlist it to iterate independently over the
> sg->pages/sg->length and sg_dma_address(sg)/sg_dma_len(sg) entries.
>
> Fixes: 42e67b479eab ("drm/prime: use dma length macro when mapping sg")
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Reviewed-by: Alex Deucher <alexander.deucher@....com>
Applied. Thanks and sorry for the breakage.
Alex
> ---
> drivers/gpu/drm/drm_prime.c | 37 +++++++++++++++++++++++++------------
> 1 file changed, 25 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 1de2cde2277c..282774e469ac 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -962,27 +962,40 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
> unsigned count;
> struct scatterlist *sg;
> struct page *page;
> - u32 len, index;
> + u32 page_len, page_index;
> dma_addr_t addr;
> + u32 dma_len, dma_index;
>
> - index = 0;
> + /*
> + * 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) {
> - len = sg_dma_len(sg);
> + page_len = sg->length;
> page = sg_page(sg);
> + dma_len = sg_dma_len(sg);
> addr = sg_dma_address(sg);
>
> - while (len > 0) {
> - if (WARN_ON(index >= max_entries))
> + while (pages && page_len > 0) {
> + if (WARN_ON(page_index >= max_entries))
> return -1;
> - if (pages)
> - pages[index] = page;
> - if (addrs)
> - addrs[index] = addr;
> -
> + pages[page_index] = page;
> page++;
> + page_len -= PAGE_SIZE;
> + page_index++;
> + }
> + while (addrs && dma_len > 0) {
> + if (WARN_ON(dma_index >= max_entries))
> + return -1;
> + addrs[dma_index] = addr;
> addr += PAGE_SIZE;
> - len -= PAGE_SIZE;
> - index++;
> + dma_len -= PAGE_SIZE;
> + dma_index++;
> }
> }
> return 0;
> --
> 2.17.1
>
> _______________________________________________
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> dri-devel@...ts.freedesktop.org
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