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

Hideki EIRAKU
2013-02-05T10:42:16Z

Joerg Roedel,

From: Joerg Roedel <joro@8bytes.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@igel.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@igel.co.jp>