Re: [PATCH 1/2] iommu: call detach also for default_domain before attaching to new one

[Marek Szyprowski <m.szyprowski-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>]

Hello,

On 2016-02-17 12:14, Joerg Roedel wrote:
> On Wed, Feb 17, 2016 at 08:35:10AM +0100, Marek Szyprowski wrote:
>> Huh, I wasn't aware of this change in the iommu drivers api. For some
>> drivers attach/detach callbacks does something more than just programming
>> page table base register, like for example in case of exynos iommu it is
>> enabling runtime power management and clocks. The code is really
>> much simpler
>> if those calls are balanced, but if the goal is to allow multiple
>> unballanced
>> attach calls, I will try to fix this in our driver.
>>
>> Maybe it should be documented somewhere, that attach calls can be
>> unbalanced?
> Well, when your driver uses default-domains, the detach_dev call-back is
> not used anymore. The attach_dev call-back is supposed to just overwrite
> any existing binding that may exist for the device. So the calls are not
> unbalanced, the detach_dev calls just don't happen anymore.

 From driver perspective the default_domains don't really differ from the
'other' domains. They are just allocated from the IOMMU core and used by
the IOMMU/DMA-mapping glue code. That's what I got from reading the code.

There should be also a way to detach the driver even from the default domain
to implement the arch_tear_down_dma_ops function.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland