linux-kernel - Re: [RFC 00/17] DRM: fix struct sg_table nents vs. orig

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Message-ID: <20200428153202.GY3456981@phenom.ffwll.local>
Date:   Tue, 28 Apr 2020 17:32:02 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Christoph Hellwig <hch@....de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        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>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        intel-gfx@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        amd-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [RFC 00/17] DRM: fix struct sg_table nents vs. orig_nents misuse

On Tue, Apr 28, 2020 at 04:02:57PM +0200, Christoph Hellwig wrote:
> On Tue, Apr 28, 2020 at 03:19:48PM +0200, Marek Szyprowski wrote:
> > 1. introduce a dma_{map,sync,unmap}_sgtable() wrappers, which will use
> >    a proper sg_table entries and call respective DMA-mapping functions
> >    and adapt current code to it
> 
> That sounds reasonable to me.  Those could be pretty trivial wrappers.
> 
> >
> > 
> > 2. rename nents and orig_nents to nr_pages, nr_dmas to clearly state
> >    which one refers to which part of the scatterlist; I'm open for
> >    other names for those entries
> 
> nr_cpu_ents and nr_dma_ents might be better names, but it still would be
> a whole lot of churn for little gain.  I think just good wrappers like
> suggested above might be more helpful.

I guess long-term we could aim for both? I.e. roll out better wrappers
first, once that's soaked through the tree, rename the last offenders.

Personally I like nr_cpu_ents and nr_dma_ents, that's about as clear as it
gets.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch