On 2022-05-04 01:52, Dmitry Osipenko wrote:
On 4/11/22 16:46, Robin Murphy wrote:
@@ -1092,6 +1092,19 @@ static bool host1x_drm_wants_iommu(struct host1x_device
*dev)
struct host1x *host1x = dev_get_drvdata(dev->dev.parent);
struct iommu_domain *domain;
+ /* For starters, this is moot if no IOMMU is available */
+ if (!device_iommu_mapped(&dev->dev))
+ return false;
Unfortunately this returns false on T30 with enabled IOMMU because we
don't use IOMMU for Host1x on T30 [1] to optimize performance. We can't
change it until we will update drivers to support Host1x-dedicated buffers.
Huh, so is dev->dev here not the DRM device? If it is, and
device_iommu_mapped() returns false, then the later iommu_attach_group()
call is going to fail anyway, so there's not much point allocating a
domain. If it's not, then what the heck is host1x_drm_wants_iommu()
actually testing for?
In the not-too-distant future we'll need to pass an appropriate IOMMU
client device to iommu_domain_alloc() as well, so the sooner we can get
this code straight the better.
Thanks,
Robin.
[1]
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/host1x/dev.c#L258
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