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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Fri, 25 Sep 2020 17:23:14 -0400
Message-ID: <CADnq5_OP4pEg7Cg9E=TUB0viSX8rTALQoFck=ueTh=phTtUfEA@mail.gmail.com>
Subject: Re: [Linaro-mm-sig] [PATCH v5 05/38] drm: prime: use sgtable
 iterators in drm_prime_sg_to_page_addr_arrays()
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     Alex Goins <agoins@nvidia.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        David Airlie <airlied@linux.ie>,
        LKML <linux-kernel@vger.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        "list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>, Joerg
        Roedel <joro@8bytes.org>," <iommu@lists.linux-foundation.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Christoph Hellwig <hch@lst.de>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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On Tue, Sep 22, 2020 at 2:28 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Alex,
>
> On 22.09.2020 01:15, Alex Goins wrote:
> > Tested-by: Alex Goins <agoins@nvidia.com>
> >
> > This change fixes a regression with drm_prime_sg_to_page_addr_arrays() and
> > AMDGPU in v5.9.
>
> Thanks for testing!
>
> > Commit 39913934 similarly revamped AMDGPU to use sgtable helper functions. When
> > it changed from dma_map_sg_attrs() to dma_map_sgtable(), as a side effect it
> > started correctly updating sgt->nents to the return value of dma_map_sg_attrs().
> > However, drm_prime_sg_to_page_addr_arrays() incorrectly uses sgt->nents to
> > iterate over pages, rather than sgt->orig_nents, resulting in it now returning
> > the incorrect number of pages on AMDGPU.
> >
> > I had written a patch that changes drm_prime_sg_to_page_addr_arrays() to use
> > for_each_sgtable_sg() instead of for_each_sg(), iterating using sgt->orig_nents:
> >
> > -       for_each_sg(sgt->sgl, sg, sgt->nents, count) {
> > +       for_each_sgtable_sg(sgt, sg, count) {
> >
> > This patch takes it further, but still has the effect of fixing the number of
> > pages that drm_prime_sg_to_page_addr_arrays() returns. Something like this
> > should be included in v5.9 to prevent a regression with AMDGPU.
>
> Probably the easiest way to handle a fix for v5.9 would be to simply
> merge the latest version of this patch also to v5.9-rcX:
> https://lore.kernel.org/dri-devel/20200904131711.12950-3-m.szyprowski@samsung.com/
>
>
> This way we would get it fixed and avoid possible conflict in the -next.
> Do you have any AMDGPU fixes for v5.9 in the queue? Maybe you can add
> that patch to the queue? Dave: would it be okay that way?

I think this should go into drm-misc for 5.9 since it's an update to
drm_prime.c.  Is that patch ready to merge?
Acked-by: Alex Deucher <alexander.deucher@amd.com>

Alex

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