On 02/02/18 05:40, Sricharan R wrote:
Hi Robin/Vivek,

On 2/1/2018 2:23 PM, Vivek Gautam wrote:
Hi,


On 1/31/2018 6:39 PM, Robin Murphy wrote:
On 19/01/18 11:43, Vivek Gautam wrote:
From: Sricharan R <sricha...@codeaurora.org>

Finally add the device link between the master device and
smmu, so that the smmu gets runtime enabled/disabled only when the
master needs it. This is done from add_device callback which gets
called once when the master is added to the smmu.

Don't we need to balance this with a device_link_del() in .remove_device (like 
exynos-iommu does)?

Right. Will add device_link_del() call. Thanks for pointing out.

  The reason for not adding device_link_del from .remove_device was, the core 
device_del
  which calls the .remove_device from notifier, calls device_links_purge before 
that.
  That does the same thing as device_link_del. So by the time .remove_device is 
called,
  device_links for that device is already cleaned up. Vivek, you may want to 
check once that
  calling device_link_del from .remove_device has no effect, just to confirm 
once more.

There is at least one path in which .remove_device is not called via the notifier from device_del(), which is in the cleanup path of iommu_bus_init(). AFAICS any links created by .add_device during that process would be left dangling, because the device(s) would be live but otherwise disassociated from the IOMMU afterwards.

From a maintenance perspective it's easier to have the call in its logical place even if it does nothing 99% of the time; that way we shouldn't have to keep an eye out for subtle changes in the power management code or driver core that might invalidate the device_del() reasoning above, and the power management guys shouldn't have to comprehend the internals of the IOMMU API to make sense of the unbalanced call if they ever want to change their API.

Thanks,
Robin.
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