ACK: [PATCH 1/1] iommu/amd: Disable IOMMU on Stoney Ridge systems

[Kleber Souza]

On 20.02.20 09:37, Kai-Heng Feng wrote:
> BugLink: https://bugs.launchpad.net/bugs/1864005
> 
> 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 at amd.com>
> Bug: https://gitlab.freedesktop.org/drm/amd/issues/961
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> Acked-by: Alex Deucher <alexander.deucher at amd.com>
> Signed-off-by: Joerg Roedel <jroedel at suse.de>
> (cherry picked from commit 3dfee47b215e49788cfc80e474820ea2e948c031)
> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>

Clean cherry-pick and fixes hardware-specific issue.

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  drivers/iommu/amd_iommu_init.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> 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 = 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;
>  		}
>