linux-kernel - Re: [PATCH v3 02/25] drm: core: fix common struct sg

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Date:   Tue, 12 May 2020 11:05:03 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Christoph Hellwig <hch@....de>
Cc:     dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        Robin Murphy <robin.murphy@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-arm-kernel@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH v3 02/25] drm: core: fix common struct sg_table related
 issues

Hi Christoph,

On 08.05.2020 09:16, Christoph Hellwig wrote:
> On Fri, May 08, 2020 at 09:12:13AM +0200, Marek Szyprowski wrote:
>> Then we would just need one more helper to construct scatterlist, as the
>> above two are read-only don't allow to modify scatterlist:
>>
>> #define for_each_sgtable_sg(sgt, sg, i)                \
>>          for_each_sg(sgt->sgl, sg, sgt->orig_nents, i)
>>
>> With the above 3 helpers we can probably get rid of all instances of
>> sg_table->{nents,orig_nents} from the DRM code. I will prepare patches soon.
> Sounds great, thanks!

It turned out that the 4th helper (for_each_sgtable_dma_sg) was needed 
as some drivers makes use of the larger than the PAGE_SIZE unit for DMA 
mapped pages.

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