linux-kernel - Re: [PATCH RFC v1 5/6] xen-swiotlb: convert variables to arrays

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Message-ID: <20210204084023.GA32328@lst.de>
Date:   Thu, 4 Feb 2021 09:40:23 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
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        x86@...nel.org, xen-devel@...ts.xenproject.org,
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        thomas.lendacky@....com
Subject: Re: [PATCH RFC v1 5/6] xen-swiotlb: convert variables to arrays

So one thing that has been on my mind for a while:  I'd really like
to kill the separate dma ops in Xen swiotlb.  If we compare xen-swiotlb
to swiotlb the main difference seems to be:

 - additional reasons to bounce I/O vs the plain DMA capable
 - the possibility to do a hypercall on arm/arm64
 - an extra translation layer before doing the phys_to_dma and vice
   versa
 - an special memory allocator

I wonder if inbetween a few jump labels or other no overhead enablement
options and possibly better use of the dma_range_map we could kill
off most of swiotlb-xen instead of maintaining all this code duplication?