Re: [v4,1/3] drm/prime: use dma length macro when mapping sg

[Alex Deucher <alexdeucher@gmail.com>]

On Mon, Mar 30, 2020 at 4:18 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi
>
> On 2020-03-27 10:10, Marek Szyprowski wrote:
> > Hi Christian,
> >
> > On 2020-03-27 09:11, Christian König wrote:
> >> Am 27.03.20 um 08:54 schrieb Marek Szyprowski:
> >>> On 2020-03-25 10:07, Shane Francis wrote:
> >>>> As dma_map_sg can reorganize scatter-gather lists in a
> >>>> way that can cause some later segments to be empty we should
> >>>> always use the sg_dma_len macro to fetch the actual length.
> >>>>
> >>>> This could now be 0 and not need to be mapped to a page or
> >>>> address array
> >>>>
> >>>> Signed-off-by: Shane Francis <bigbeeshane@gmail.com>
> >>>> Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
> >>> This patch landed in linux-next 20200326 and it causes a kernel
> >>> panic on
> >>> various Exynos SoC based boards.
> >>>> ---
> >>>>    drivers/gpu/drm/drm_prime.c | 2 +-
> >>>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> >>>> index 86d9b0e45c8c..1de2cde2277c 100644
> >>>> --- a/drivers/gpu/drm/drm_prime.c
> >>>> +++ b/drivers/gpu/drm/drm_prime.c
> >>>> @@ -967,7 +967,7 @@ int drm_prime_sg_to_page_addr_arrays(struct
> >>>> sg_table *sgt, struct page **pages,
> >>>>           index = 0;
> >>>>        for_each_sg(sgt->sgl, sg, sgt->nents, count) {
> >>>> -        len = sg->length;
> >>>> +        len = sg_dma_len(sg);
> >>>>            page = sg_page(sg);
> >>>>            addr = sg_dma_address(sg);
> >>> Sorry, but this code is wrong :(
> >>
> >> Well it is at least better than before because it makes most drivers
> >> work correctly again.
> >
> > Well, I'm not sure that a half-broken fix should be considered as a
> > fix ;)
> >
> > Anyway, I just got the comment from Shane, that my patch is fixing the
> > issues with amdgpu and radeon, while still working fine for exynos, so
> > it is indeed a proper fix.
>
> Today I've noticed that this patch went to final v5.6 without even a day
> of testing in linux-next, so v5.6 is broken on Exynos and probably a few
> other ARM archs, which rely on the drm_prime_sg_to_page_addr_arrays
> function.

Please commit your patch and cc stable.

Alex


>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>
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