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Date:   Thu, 29 Nov 2018 19:31:32 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
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        David Woodhouse <dwmw2@infradead.org>,
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Subject: Re: remove the ->mapping_error method from dma_map_ops V2
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On Thu, Nov 29, 2018 at 09:44:05AM -0800, Linus Torvalds wrote:
> No. Really. If there's no iotlb, then you just mark that one page
> reserved. It simply doesn't get used. It doesn't mean you suddenly
> need a swiotlb.

Sure, we could just skip that page entirely based on dma_to_phys.

> But whatever. It's independent from the patch series under discussion.
> Make dma_mapping_error() at least return a real error (eg -EINVAL, or
> whatever is the common error), and we can maybe do this later.

Ok, I'll do that.

> Or, better yet, plan on removing the single-page dma mappign entirely
> at a later date, and make the issue moot.

What would be the replacement?  Build a S/G list for every single page
mapping?  Not sure that would create a lot of happy campers..