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

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Message-Id: <974A8EB3-70B6-4A33-B36C-CFF69464493C@canonical.com>
Date:   Fri, 6 Dec 2019 13:57:41 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Alex Deucher <alexander.deucher@....com>,
        iommu@...ts.linux-foundation.org,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iommu/amd: Disable IOMMU on Stoney Ridge systems

Hi Joerg,

> On Dec 3, 2019, at 01:00, Christoph Hellwig <hch@...radead.org> 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