linux-kernel - Re: remove the ->mapping_error method from dma_map

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Date:   Fri, 23 Nov 2018 14:03:13 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Robin Murphy <robin.murphy@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-alpha@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, jdmason@...zu.us,
        xen-devel@...ts.xenproject.org,
        linux-arm-kernel@...ts.infradead.org, m.szyprowski@...sung.com
Subject: Re: remove the ->mapping_error method from dma_map_ops V2

On Fri, Nov 23, 2018 at 11:01:55AM +0000, Russell King - ARM Linux wrote:
> Yuck.  So, if we have a 4GB non-PAE 32-bit system, or a PAE system
> where we have valid memory across the 4GB boundary and no IOMMU,
> we have to reserve the top 4K page in the first 4GB of RAM?

But that is only needed when dma_addr_t is 32bit anyway, no?

> Rather than inventing magic cookies like this, I'd much rather we
> sanitised the API so that we have functions that return success or
> an error code, rather than trying to shoe-horn some kind of magic
> error codes into dma_addr_t and subtly break systems in the process.

Sure, but is has the obvious downside that we need to touch every driver
that uses these functions, and that are probably a lot of drivers.


Regards,

	Joerg