linux-kernel - Re: [PATCH V3] PCI: Extend ACS configurability

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Message-ID: <20240612121941.GZ19897@nvidia.com>
Date: Wed, 12 Jun 2024 09:19:41 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Vidya Sagar <vidyas@...dia.com>
Cc: corbet@....net, bhelgaas@...gle.com, galshalom@...dia.com,
	leonro@...dia.com, treding@...dia.com, jonathanh@...dia.com,
	mmoshrefjava@...dia.com, shahafs@...dia.com, vsethi@...dia.com,
	sdonthineni@...dia.com, jan@...dia.com, tdave@...dia.com,
	linux-doc@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, kthota@...dia.com,
	mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V3] PCI: Extend ACS configurability

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@...dia.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@...dia.com>

Jason