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


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