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

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Message-ID: <CAAFQd5DpXxyoNiTGC4YYnpXeKo43XXrC+my6KWOV1pGq1jw6Aw@mail.gmail.com>
Date:	Tue, 10 Mar 2015 02:00:44 +0900
From:	Tomasz Figa <tfiga@...omium.org>
To:	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Joerg Roedel <joro@...tes.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>,
	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, Mar 9, 2015 at 11:46 PM, Yingjoe Chen <yingjoe.chen@...iatek.com> wrote:
> 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*.

Looking at how already mainlined drivers do this, they either use
dmac_flush_range()
(https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/msm_iommu.c?id=refs/tags/v4.0-rc3#n80)
or directly __cpuc_flush_dcache_area() and outer_flush_range()
(https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/rockchip-iommu.c?id=refs/tags/v4.0-rc3#n93).

Joerg, what's your opinion on this?

Best regards,
Tomasz
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