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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 31 Mar 2020 10:10:17 -0400
Message-ID: <CADnq5_NEhfZwE6B0UBu0My7Sk5YNoDE=7Nj_CUYpPe9HOjpjqQ@mail.gmail.com>
Subject: Re: [v4,1/3] drm/prime: use dma length macro when mapping sg
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        Shane Francis <bigbeeshane@gmail.com>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>, Dave Airlie <airlied@linux.ie>,
        "Deucher, Alexander" <alexander.deucher@amd.com>,
        LKML <linux-kernel@vger.kernel.org>,
        amd-gfx-request@lists.freedesktop.org
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On Tue, Mar 31, 2020 at 1:25 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Alex,
>
> On 2020-03-30 15:23, Alex Deucher wrote:
> > 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 K=C3=B6nig 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_pri=
me.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 =3D 0;
> >>>>>>         for_each_sg(sgt->sgl, sg, sgt->nents, count) {
> >>>>>> -        len =3D sg->length;
> >>>>>> +        len =3D sg_dma_len(sg);
> >>>>>>             page =3D sg_page(sg);
> >>>>>>             addr =3D 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 th=
e
> >>> issues with amdgpu and radeon, while still working fine for exynos, s=
o
> >>> it is indeed a proper fix.
> >> Today I've noticed that this patch went to final v5.6 without even a d=
ay
> >> of testing in linux-next, so v5.6 is broken on Exynos and probably a f=
ew
> >> other ARM archs, which rely on the drm_prime_sg_to_page_addr_arrays
> >> function.
> > Please commit your patch and cc stable.
>
> I've already did that: https://lkml.org/lkml/2020/3/27/555

Do you have drm-misc commit rights or do you need someone to commit
this for you?

Alex


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