linux-kernel - Re: [PATCH v6 1/4] iommu/shmobile: Add iommu driver for Renesas IPMMU modules

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Date:	Wed, 6 Feb 2013 11:23:50 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Hideki EIRAKU <hdk@...l.co.jp>
Cc:	lethal@...ux-sh.org, magnus.damm@...il.com, linux@....linux.org.uk,
	horms@...ge.net.au, laurent.pinchart@...asonboard.com,
	matsu@...l.co.jp, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	dhobsong@...l.co.jp, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 1/4] iommu/shmobile: Add iommu driver for Renesas
 IPMMU modules

On Tue, Feb 05, 2013 at 07:42:09PM +0900, Hideki EIRAKU wrote:
> From: Joerg Roedel <joro@...tes.org>

> > Why is it necessary to call dma_map_single() for IOMMU page-tables?
> > usually the dma_* functions call into IOMMU drivers, so why are they
> > used inside an IOMMU driver?
> 
> I use dma_map_single() for flushing the page table to the IOMMU
> device.  The dma_map_ops set by arch/arm/mm/dma-mapping.c are
> per-device (unlike the intel-iommu).  The dma_* functions call into
> IOMMU drivers if the device is attached by arm_iommu_attach_device(),
> but I am using a NULL device here, so that shouldn't happen.

Okay, I applied the patches to a new arm/shmobile branch. Will push them
out soon. The use of the dma_* functions is dangerous anyway (but it
works for now). Please send a follow-on patch to replace the use of the
dma_* functions in the driver with explicit flushing routines. This
protects the code from any future changes in the dma-api implementation.


	Joerg


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