Re: [PATCH 2/5] iommu/mediatek: Add mt8173 IOMMU driver

[Tomasz Figa]

On Mon, Mar 9, 2015 at 11:46 PM, Yingjoe Chen <yingjoe.chen@xxxxxxxxxxxx> wrote:
> On Mon, 2015-03-09 at 20:11 +0900, Tomasz Figa wrote:
> <...>
>> > +/*
>> > + * pimudev is a global var for dma_alloc_coherent.
>> > + * It is not accepatable, we will delete it if "domain_alloc" is enabled
>> > + */
>> > +static struct device *pimudev;
>>
>> This is indeed not acceptable. Could you replace dma_alloc_coherent()
>> with something that doesn't require device pointer, e.g.
>> alloc_pages()? (Although that would require you to handle cache
>> maintenance in the driver, due to cached memory allocated.) I need to
>> think about a better solution for this.
>
> Hi,
>
> For 2nd level page table, we use cached memory now. Currently we are
> using __dma_flush_range to flush the cache, which is also unacceptable.
>
> For proper cache management, we'll need to use dma_map_single or
> dma_sync_*, which still need a deivce*.

Looking at how already mainlined drivers do this, they either use
dmac_flush_range()
(https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/msm_iommu.c?id=refs/tags/v4.0-rc3#n80)
or directly __cpuc_flush_dcache_area() and outer_flush_range()
(https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/rockchip-iommu.c?id=refs/tags/v4.0-rc3#n93).

Joerg, what's your opinion on this?

Best regards,
Tomasz
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