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

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Date:   Wed, 30 Sep 2020 09:15:29 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Alex Deucher <alexdeucher@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <mripard@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Alex Goins <agoins@...dia.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        LKML <linux-kernel@...r.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Linaro-mm-sig] [PATCH v5 05/38] drm: prime: use sgtable
 iterators in drm_prime_sg_to_page_addr_arrays()

Hi All,

On 25.09.2020 23:23, Alex Deucher wrote:
> On Tue, Sep 22, 2020 at 2:28 AM Marek Szyprowski
> <m.szyprowski@...sung.com> wrote:
>> 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?
> 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@....com>

Maarten, Maxime or Thomas: could you take this one:

https://lore.kernel.org/dri-devel/20200904131711.12950-3-m.szyprowski@samsung.com/

also to drm-misc-fixes for v5.9-rc?

Best regards

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