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iommu/amd: Disable IOMMU on Stoney Ridge systems 

Serious screen flickering when Stoney Ridge outputs to a 4K monitor.

Use identity-mapping and PCI ATS doesn't help this issue.

According to Alex Deucher, IOMMU isn't enabled on Windows, so let's do
the same here to avoid screen flickering on 4K monitor.

Cc: Alex Deucher <alexander.deucher@amd.com>
Bug: https://gitlab.freedesktop.org/drm/amd/issues/961
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
alistair/sensors
Kai-Heng Feng 2020-02-10 15:51:15 +08:00 committed by Joerg Roedel
parent 1ddb32da4a
commit 3dfee47b21
1 changed files with 12 additions and 1 deletions
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13
drivers/iommu/amd_iommu_init.c
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@ -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 = 0;
u32 pci_id;
if (!amd_iommu_detected)
return -ENODEV;
@ -2610,6 +2611,16 @@ static int __init early_amd_iommu_init(void)
if (ret)
goto out;
/* Disable IOMMU if there's Stoney Ridge graphics */
for (i = 0; i < 32; i++) {
pci_id = read_pci_config(0, i, 0, 0);
if ((pci_id & 0xffff) == 0x1002 && (pci_id >> 16) == 0x98e4) {
pr_info("Disable IOMMU on Stoney Ridge\n");
amd_iommu_disabled = 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 = early_amd_iommu_init();
init_state = ret ? IOMMU_INIT_ERROR : IOMMU_ACPI_FINISHED;
if (init_state == IOMMU_ACPI_FINISHED && amd_iommu_disabled) {
pr_info("AMD IOMMU disabled on kernel command-line\n");
pr_info("AMD IOMMU disabled\n");
init_state = IOMMU_CMDLINE_DISABLED;
ret = -EINVAL;
}