linux-kernel - Re: [PATCH v5 05/38] drm: prime: use sgtable iterators in drm_prime_sg_to_page_addr

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Date:   Tue, 22 Sep 2020 16:12:49 -0500
From:   Alex Goins <agoins@...dia.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
CC:     <dri-devel@...ts.freedesktop.org>,
        <iommu@...ts.linux-foundation.org>,
        <linaro-mm-sig@...ts.linaro.org>, <linux-kernel@...r.kernel.org>,
        "Thomas Zimmermann" <tzimmermann@...e.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 05/38] drm: prime: use sgtable iterators in
 drm_prime_sg_to_page_addr_arrays()

Hi Marek,

On Tue, 22 Sep 2020, Marek Szyprowski wrote:

> External email: Use caution opening links or attachments
> 
> 
> Hi Alex,
> 
> On 22.09.2020 01:15, Alex Goins wrote:
> > Tested-by: Alex Goins <agoins@...dia.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/

Tested-by: Alex Goins <agoins@...dia.com> that version too.

> 
> 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? 

I don't have any more AMDGPU fixes, just want to ensure that this makes it in.

Thanks,
Alex

> Dave: would it be okay that way?
> 
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 
>