linux-kernel - Re: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver

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Message-ID: <1425912389.4871.19.camel@mtksdaap41>
Date:	Mon, 9 Mar 2015 22:46:29 +0800
From:	Yingjoe Chen <yingjoe.chen@...iatek.com>
To:	Tomasz Figa <tfiga@...omium.org>
CC:	Yong Wu (吴勇) 
	<yong.wu@...iatek.com>, Mark Rutland <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <srv_heupstream@...iatek.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<iommu@...ts.linux-foundation.org>,
	Rob Herring <robh+dt@...nel.org>,
	Daniel Kurtz <djkurtz@...gle.com>,
	Sasha Hauer <kernel@...gutronix.de>,
	Matthias Brugger <matthias.bgg@...il.com>,
	<linux-mediatek@...ts.infradead.org>,
	Robin Murphy <robin.murphy@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lucas Stach <l.stach@...gutronix.de>
Subject: Re: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver

On Mon, 2015-03-09 at 20:11 +0900, Tomasz Figa wrote:
<...>
> > +/*
> > + * pimudev is a global var for dma_alloc_coherent.
> > + * It is not accepatable, we will delete it if "domain_alloc" is enabled
> > + */
> > +static struct device *pimudev;
> 
> This is indeed not acceptable. Could you replace dma_alloc_coherent()
> with something that doesn't require device pointer, e.g.
> alloc_pages()? (Although that would require you to handle cache
> maintenance in the driver, due to cached memory allocated.) I need to
> think about a better solution for this.

Hi,

For 2nd level page table, we use cached memory now. Currently we are
using __dma_flush_range to flush the cache, which is also unacceptable.

For proper cache management, we'll need to use dma_map_single or
dma_sync_*, which still need a deivce*.

Joe.C


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