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

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Message-ID: <afb59d1b-1fcf-fd6d-2b48-e078e129f1eb@samsung.com>
Date:   Tue, 22 Sep 2020 08:27:58 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Alex Goins <agoins@...dia.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 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/ 


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?

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