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

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Date:   Tue, 31 Mar 2020 16:29:09 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Alex Deucher <alexdeucher@...il.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

Hi Alex,

On 2020-03-31 16:10, Alex Deucher wrote:
> 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%3A%2F%2Flkml.org%2Flkml%2F2020%2F3%2F27%2F555
> Do you have drm-misc commit rights or do you need someone to commit
> this for you?

I have no access to drm-misc.

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