Hello,
On 2016-02-16 16:59, Joerg Roedel wrote:
On Tue, Feb 16, 2016 at 03:40:31PM +0100, Marek Szyprowski wrote:
This patch ensures that devices attached to the default_domain will be
first detached from it before attaching to new domain. To avoid forward
declaration, __iommu_attach_group() function has been moved to new place
in the source code.
Actually it was intentional to not invoke the detach_device call-back in
the attach_device path.
The reason is that detaching first and than attaching again leaves the
device without a domain for a short period of time, until it is attached
to the new domain.
The attach_device call-back is supposed to handle this situation and
just silently overwrite any other domain->device binding it finds for
the device.
This allows to do re-attachment with less iommu flushes and to get rid
of the detach_device call-back at some point.
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?
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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