linux-kernel - Re: [Xen-devel] [PATCH 07/11] swiotlb-xen: provide a single page-coherent.h header

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Message-ID: <20190817065011.GA18599@lst.de>
Date:   Sat, 17 Aug 2019 08:50:11 +0200
From:   Christoph Hellwig <hch@....de>
To:     Julien Grall <julien.grall@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [Xen-devel] [PATCH 07/11] swiotlb-xen: provide a single
 page-coherent.h header

On Fri, Aug 16, 2019 at 11:40:43PM +0100, Julien Grall wrote:
> I am not sure I agree with this rename. The implementation of the helpers 
> are very Arm specific as this is assuming Dom0 is 1:1 mapped.
>
> This was necessary due to the lack of IOMMU on Arm platforms back then.
> But this is now a pain to get rid of it on newer platform...

So if you look at the final version of the header after the whole
series, what assumes a 1:1 mapping?  It all just is

	if (pfn_valid())
		local cache sync;
	else
		call into the arch code;

are you concerned that the local cache sync might have to be split
up more for a non-1:1 map in that case?  We could just move
the xen_dma_* routines into the arch instead of __xen_dma, but it
really helps to have a common interface header.