Re: [PATCH V3] PCI: Extend ACS configurability

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, May 23, 2024 at 12:05:28PM +0530, Vidya Sagar wrote:
> For iommu_groups to form correctly, the ACS settings in the PCIe fabric
> need to be setup early in the boot process, either via the BIOS or via
> the kernel disable_acs_redir parameter.
> 
> disable_acs_redir allows clearing the RR|CR|EC ACS flags, but the PCIe
> spec Rev3.0 already defines 7 different ACS related flags with many more
> useful combinations depending on the fabric design.
> 
> For backward compatibility, leave the 'disable_acs_redir' as is and add
> a new parameter 'config_acs'so that the user can directly specify the ACS
> flags to set on a per-device basis. Use a similar syntax to the existing
> 'resource_alignment'  parameter by using the @ character and have the user
> specify the ACS flags using a bit encoding. If both 'disable_acs_redir' and
> 'config_acs' are specified for a particular device, configuration specified
> through 'config_acs' takes precedence over the other.
> 
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
> v3:
> * Fixed a documentation issue reported by kernel test bot
> 
> v2:
> * Refactored the code as per Jason's suggestion

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason