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.

[1]
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/host1x/dev.c#L258

-- 
Best regards,
Dmitry
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