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

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Date:	Tue, 05 Feb 2013 19:42:09 +0900 (JST)
From:	Hideki EIRAKU <hdk@...l.co.jp>
To:	joro@...tes.org
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

Joerg Roedel,

From: Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v6 1/4] iommu/shmobile: Add iommu driver for Renesas IPMMU modules
Date: Fri, 1 Feb 2013 14:54:57 +0100

> On Mon, Jan 21, 2013 at 07:54:26PM +0900, Hideki EIRAKU wrote:
>> This is the Renesas IPMMU driver and IOMMU API implementation.
>> 
>> The IPMMU module supports the MMU function and the PMB function.  The
>> MMU function provides address translation by pagetable compatible with
>> ARMv6.  The PMB function provides address translation including
>> tile-linear translation.  This patch implements the MMU function.
>> 
>> The iommu driver does not register a platform driver directly because:
>> - the register space of the MMU function and the PMB function
>>   have a common register (used for settings flush), so they should ideally
>>   have a way to appropriately share this register.
>> - the MMU function uses the IOMMU API while the PMB function does not.
>> - the two functions may be used independently.
>> 
>> Signed-off-by: Hideki EIRAKU <hdk@...l.co.jp>
> 
> The patch looks good in general. Just one question inline.
> 
>> +static int pgtable_alloc(struct shmobile_iommu_domain_pgtable *pgtable,
>> +			 struct kmem_cache *cache, size_t size)
>> +{
>> +	pgtable->pgtable = kmem_cache_zalloc(cache, GFP_ATOMIC);
>> +	if (!pgtable->pgtable)
>> +		return -ENOMEM;
>> +	pgtable->handle = dma_map_single(NULL, pgtable->pgtable, size,
>> +					 DMA_TO_DEVICE);
>> +	return 0;
>> +}
> 
> 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.

-- 
Hideki EIRAKU <hdk@...l.co.jp>
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