From mboxrd@z Thu Jan  1 00:00:00 1970
From: robin.murphy@arm.com (Robin Murphy)
Date: Mon, 27 Jul 2015 16:49:30 +0100
Subject: [PATCH v3 5/6] iommu/mediatek: Add mt8173 IOMMU driver
In-Reply-To: <20150727153148.GJ7557@n2100.arm.linux.org.uk>
References: <1437037475-9065-1-git-send-email-yong.wu@mediatek.com>
 <1437037475-9065-6-git-send-email-yong.wu@mediatek.com>
 <55B630CE.4050803@arm.com> <20150727153148.GJ7557@n2100.arm.linux.org.uk>
Message-ID: <55B6530A.9050903@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 27/07/15 16:31, Russell King - ARM Linux wrote:
> On Mon, Jul 27, 2015 at 02:23:26PM +0100, Robin Murphy wrote:
>> On 16/07/15 10:04, Yong Wu wrote:
>>> This patch adds support for mediatek m4u (MultiMedia Memory Management
>>> Unit).
>>>
>>> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
>> [...]
>>> +static void mtk_iommu_flush_pgtable(void *ptr, size_t size, void *cookie)
>>> +{
>>> +       struct mtk_iommu_domain *domain = cookie;
>>> +       unsigned long offset = (unsigned long)ptr & ~PAGE_MASK;
>>> +
>>> +       dma_map_page(domain->data->dev, virt_to_page(ptr), offset,
>>> +                    size, DMA_TO_DEVICE);
>>
>> Nit: this looks like it may as well be dma_map_single.
>>
>> It would probably be worth following it with a matching unmap too, just to
>> avoid any possible leakage bugs (especially if this M4U ever appears in a
>> SoC supporting RAM above the 32-bit boundary).
>
> Why not do the job properly?  Take a look at how I implemented the
> streaming DMA API on Tegra SMMU (patch set recently sent out earlier
> today).
>
> There's no need for hacks like dma_map_page() (and discarding it's
> return value) or dma_map_page() followed by dma_unmap_page().

Indeed, as it happens I do have a branch where I prototyped that for the 
long-descriptor io-pgtable-arm code a while ago; this discussion has 
prompted me to dig it up again. Stay tuned, folks...

Robin.