Re: [PATCH v2 1/1] iommu/amd: Enable PCIe ACS only if AMD IOMMU is on

[Jörg Rödel]

On Sat, Oct 11, 2025 at 11:14:48AM +0800, Jinhui Guo wrote:
> To preserve PCIe performance, ACS is enabled only when
> AMD IOMMU is not disabled.
> 
> Signed-off-by: Jinhui Guo <guojinhui.liam@xxxxxxxxxxxxx>
> Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> ---
>  drivers/iommu/amd/init.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index f2991c11867c..38e8c38c5f10 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3314,8 +3314,10 @@ static bool __init detect_ivrs(void)
>  	}
>  
>  out:
> -	/* Make sure ACS will be enabled during PCI probe */
> -	pci_request_acs();
> +	if (!amd_iommu_disabled) {
> +		/* Make sure ACS will be enabled during PCI probe */
> +		pci_request_acs();
> +	}

Instead of checking amd_iommu_disabled here it is better to move the
pci_request_acs() call to early_amd_iommu_init(). This function is only called
when amd_iommu_disabled is false and runs still before PCI probing.

Regards,

	Joerg