linux-kernel - Re: [PATCH v2 2/4] ARC: allow to use IOC and non-IOC DMA devices simultaneously

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Date:   Thu, 23 Aug 2018 16:05:25 +0200
From:   "hch@....de" <hch@....de>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:     Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>, "hch@....de" <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>
Subject: Re: [PATCH v2 2/4] ARC: allow to use IOC and non-IOC DMA devices
 simultaneously

Btw, given that I assume this is 4.20 material now, any chance we
could merge it through the dma-mapping tree?  I have some major changes
pending that would clash if done in a different tree, so I'd rather
get it all together.

> We check this flag in arch_dma_alloc (which are used in non-coherent case) to
> skip MMU mapping if we are advertised that consistency is not required.
> 
> So, actually we can get rid of this flag checking in arch_dma_alloc and 
> simply always do MMU mapping to enforce non-cachability and return
> non-cacheable memory even if DMA_ATTR_NON_CONSISTENT is passed.
> But I don't sure we want to do that.

I plan to kill this flag for 4.20 (or 4.20 at latest) in favor
of a better interface.  But your implementation looks ok, so I'm
fine with keeping it for now.