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

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Date:   Tue, 31 Mar 2020 10:10:17 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Christian König <christian.koenig@....com>,
        Shane Francis <bigbeeshane@...il.com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>, Dave Airlie <airlied@...ux.ie>,
        "Deucher, Alexander" <alexander.deucher@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx-request@...ts.freedesktop.org
Subject: Re: [v4,1/3] drm/prime: use dma length macro when mapping sg

On Tue, Mar 31, 2020 at 1:25 AM Marek Szyprowski
<m.szyprowski@...sung.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@...sung.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@...il.com>
> >>>>>> Reviewed-by: Michael J. Ruhl <michael.j.ruhl@...el.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.
>
> 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
>