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Date: Wed, 12 Jun 2024 09:19:41 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Vidya Sagar <vidyas@nvidia.com>
Cc: corbet@lwn.net, bhelgaas@google.com, galshalom@nvidia.com,
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Subject: Re: [PATCH V3] PCI: Extend ACS configurability
Message-ID: <20240612121941.GZ19897@nvidia.com>
References: <20240521110925.3876786-1-vidyas@nvidia.com>
 <20240523063528.199908-1-vidyas@nvidia.com>
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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