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Date:   Tue, 5 May 2020 13:09:50 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     Christoph Hellwig <hch@lst.de>, dri-devel@lists.freedesktop.org,
        iommu@lists.linux-foundation.org, linaro-mm-sig@lists.linaro.org,
        linux-kernel@vger.kernel.org, Robin Murphy <robin.murphy@arm.com>,
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        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>
Subject: Re: [PATCH v3 02/25] drm: core: fix common struct sg_table related
 issues
Message-ID: <20200505110950.GA19067@lst.de>
References: <20200505083926.28503-1-m.szyprowski@samsung.com> <20200505084614.30424-1-m.szyprowski@samsung.com> <CGME20200505084625eucas1p1a3c25fd171f360e0aab2f76700699454@eucas1p1.samsung.com> <20200505084614.30424-2-m.szyprowski@samsung.com> <20200505101508.GA14860@lst.de> <5dd1cb55-accb-0dc6-4ca5-90c57cd19527@samsung.com>
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On Tue, May 05, 2020 at 12:51:58PM +0200, Marek Szyprowski wrote:
> Hi Christoph,
> 
> On 05.05.2020 12:15, Christoph Hellwig wrote:
> >> -		for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
> >> +		for_each_sg_page(st->sgl, &sg_iter, st->orig_nents, 0)
> > Would it make sense to also add a for_each_sgtable_page helper that
> > hides the use of orig_nents?  To be used like:
> >
> > 		for_each_sgtable_page(st, &sg_iter, 0) {
> 
> We would need two helpers:
> 
> for_each_sgtable_cpu_page() and for_each_sgtable_dma_page().
> 
> I considered them, but then I found that there are already 
> for_each_sg_page(), for_each_sg_dma_page() and various special iterators 
> like sg_page_iter, sg_dma_page_iter and sg_mapping_iter. Too bad that 
> they are almost not used, at least in the DRM subsystem. I wonder if it 
> make sense to apply them or simply provide the two above mentioned 
> wrappers?

None of the helpers helps with passing the right parameters from the
sg_table.  So in doube we'd need wrappers for all of the above, or
none..