On Wed, Feb 14, 2018 at 10:48 AM, Jordan Crouse [off-list ref] wrote:

On Wed, Feb 14, 2018 at 12:31:29PM +0900, Tomasz Figa wrote:

quoted

- When submitting commands to the GPU, the GPU driver will
pm_runtime_get_sync() on the GPU device, which will automatically do
the same on all the linked suppliers, which would also include the
SMMU itself. The role of device links here is exactly that the GPU
driver doesn't have to care which other devices need to be brought up.

This is true.  Assuming that the device link works correctly we would not need
to explicitly power the SMMU which makes my point entirely moot.

Just to point out what motivated this patchset, the biggest problem is
iommu_unmap() because that can happen when GPU is not powered on (or
in the v4l2 case, because some other device dropped it's reference to
the dma-buf allowing it to be free'd).  Currently we pm get/put the
GPU device around unmap, but it is kinda silly to boot up the GPU just
to unmap a buffer.

(Semi-related, I would also like to batch map/unmap's, I just haven't
gotten around to implementing it yet.. but that would be another case
where a single get_supplier()/put_supplier() outside of the iommu
would make sense instead of pm_get/put() inside the iommu driver's
->unmap().)

If you really dislike the get/put_supplier() approach, then perhaps we
need iommu_pm_get()/iommu_pm_put() operations that the iommu user
could use to accomplish the same thing?

BR,
-R
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