On 30/04/18 13:12, Thierry Reding wrote:
On Mon, Apr 30, 2018 at 12:41:52PM +0100, Robin Murphy wrote:
On 30/04/18 12:02, Thierry Reding wrote:
On Thu, Apr 26, 2018 at 02:11:36PM +0200, Thierry Reding wrote:
On Wed, Apr 25, 2018 at 08:19:34AM -0700, Christoph Hellwig wrote:
On Wed, Apr 25, 2018 at 12:10:48PM +0200, Thierry Reding wrote:
From: Thierry Reding <treding@xxxxxxxxxx>
The dma_iommu_detach_device() API can be used by drivers to forcibly
detach a device from an IOMMU that architecture code might have attached
to. This is useful for drivers that need explicit control over the IOMMU
using the IOMMU API directly.
Given that no one else implements it making it a generic API seems
rather confusing. For now I'd rename it to
arm_dma_iommu_detach_device() and only implement it in arm.
That'd be suboptimal because this code is used on both 32-bit and 64-bit
ARM. If we make the function 32-bit ARM specific then the driver code
would need to use an #ifdef to make sure compilation doesn't break on
64-bit ARM.
Do you still want me to make this ARM specific? While I haven't
encountered this issue on 64-bit ARM yet, I think it would happen there
as well, under the right circumstances. I could take a shot at
implementing the equivalent there (which means essentially implementing
it for drivers/iommu/dma-iommu.c and calling that from 64-bit ARM code).
It sounds like things are getting a bit backwards here: iommu-dma should
have nothing to do with this, since if you've explicitly attached the device
to your own IOMMU domain then you're already bypassing everything it knows
about and has control over. Arch code calling into iommu-dma to do something
which makes arch code not use iommu-dma makes very little sense.
My understanding is that iommu-dma will set up an IOMMU domain at device
probe time anyway. So even if attaching to an own IOMMU domain will end
up bypassing iommu-dma, we'd still want to clear up the IOMMU domain and
any associated resources, right?
The lifetime of a "proper" IOMMU API default domain is that of the
iommu_group, so more or less between device_add() and device_del() from
the perspective of a device in that group. IOW at least one level below
what that device's driver should be messing with. The domain itself is
just a little bit of memory and shouldn't have to occupy any hardware
resources while it's not active (and yes, I know the ARM SMMU driver is
currently a bit crap in that regard).
Robin.
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