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From:   "Deucher, Alexander" <Alexander.Deucher@amd.com>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>,
        "joro@8bytes.org" <joro@8bytes.org>
CC:     "open list:AMD IOMMU (AMD-VI)" <iommu@lists.linux-foundation.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v3] iommu/amd: Disable IOMMU on Stoney Ridge systems
Thread-Topic: [PATCH v3] iommu/amd: Disable IOMMU on Stoney Ridge systems
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Date:   Mon, 10 Feb 2020 15:16:12 +0000
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References: <20200210075115.14838-1-kai.heng.feng@canonical.com>
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[AMD Public Use]

> -----Original Message-----
> From: Kai-Heng Feng <kai.heng.feng@canonical.com>
> Sent: Monday, February 10, 2020 2:51 AM
> To: joro@8bytes.org
> Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>; Deucher, Alexander
> <Alexander.Deucher@amd.com>; open list:AMD IOMMU (AMD-VI)
> <iommu@lists.linux-foundation.org>; open list <linux-
> kernel@vger.kernel.org>
> Subject: [PATCH v3] iommu/amd: Disable IOMMU on Stoney Ridge systems
>=20
> Serious screen flickering when Stoney Ridge outputs to a 4K monitor.
>=20
> Use identity-mapping and PCI ATS doesn't help this issue.
>=20
> According to Alex Deucher, IOMMU isn't enabled on Windows, so let's do th=
e
> same here to avoid screen flickering on 4K monitor.
>=20
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Bug:
> https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fgitla
> b.freedesktop.org%2Fdrm%2Famd%2Fissues%2F961&amp;data=3D02%7C01%7
> Calexander.deucher%40amd.com%7C79aa213aaf2d4540064308d7adfe0749%
> 7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637169178877965485
> &amp;sdata=3DUeNw4%2FuQ3Rs5SwEvguDmdfuMEsizO8F138B%2B2GNleTY%
> 3D&amp;reserved=3D0
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>

Acked-by: Alex Deucher <alexander.deucher@amd.com>


> ---
> v3:
>  - Update commit message to mention identity-mapping and ATS don't help.
>=20
> v2:
>  - Find Stoney graphics instead of host bridge.
>=20
>  drivers/iommu/amd_iommu_init.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/iommu/amd_iommu_init.c
> b/drivers/iommu/amd_iommu_init.c index 2759a8d57b7f..6be3853a5d97
> 100644
> --- a/drivers/iommu/amd_iommu_init.c
> +++ b/drivers/iommu/amd_iommu_init.c
> @@ -2523,6 +2523,7 @@ static int __init early_amd_iommu_init(void)
>  	struct acpi_table_header *ivrs_base;
>  	acpi_status status;
>  	int i, remap_cache_sz, ret =3D 0;
> +	u32 pci_id;
>=20
>  	if (!amd_iommu_detected)
>  		return -ENODEV;
> @@ -2610,6 +2611,16 @@ static int __init early_amd_iommu_init(void)
>  	if (ret)
>  		goto out;
>=20
> +	/* Disable IOMMU if there's Stoney Ridge graphics */
> +	for (i =3D 0; i < 32; i++) {
> +		pci_id =3D read_pci_config(0, i, 0, 0);
> +		if ((pci_id & 0xffff) =3D=3D 0x1002 && (pci_id >> 16) =3D=3D 0x98e4) {
> +			pr_info("Disable IOMMU on Stoney Ridge\n");
> +			amd_iommu_disabled =3D true;
> +			break;
> +		}
> +	}
> +
>  	/* Disable any previously enabled IOMMUs */
>  	if (!is_kdump_kernel() || amd_iommu_disabled)
>  		disable_iommus();
> @@ -2718,7 +2729,7 @@ static int __init state_next(void)
>  		ret =3D early_amd_iommu_init();
>  		init_state =3D ret ? IOMMU_INIT_ERROR :
> IOMMU_ACPI_FINISHED;
>  		if (init_state =3D=3D IOMMU_ACPI_FINISHED &&
> amd_iommu_disabled) {
> -			pr_info("AMD IOMMU disabled on kernel command-
> line\n");
> +			pr_info("AMD IOMMU disabled\n");
>  			init_state =3D IOMMU_CMDLINE_DISABLED;
>  			ret =3D -EINVAL;
>  		}
> --
> 2.17.1