Re: [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge systems

[Kai-Heng Feng]

Hi Joerg,

> On Dec 3, 2019, at 01:00, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> 
> On Fri, Nov 29, 2019 at 10:21:54PM +0800, Kai-Heng Feng wrote:
>> Serious screen flickering when Stoney Ridge outputs to a 4K monitor.
>> 
>> According to Alex Deucher, IOMMU isn't enabled on Windows, so let's do
>> the same here to avoid screen flickering on 4K monitor.
> 
> Disabling the IOMMU entirely seem pretty severe.  Isn't it enough to
> identity map the GPU device?

Ok, there's set_device_exclusion_range() to exclude the device from IOMMU.
However I don't know how to generate range_start and range_length, which are read from ACPI.

Can you please give me some advice here?

Kai-Henge