linux-kernel - Re: [PATCH v10 1/3] iommu: Enhance IOMMU default DMA mode build options

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Date:   Thu, 3 Jun 2021 10:00:34 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
        robin.murphy@....com
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linuxarm@...wei.com, thunder.leizhen@...wei.com,
        chenxiang66@...ilicon.com
Subject: Re: [PATCH v10 1/3] iommu: Enhance IOMMU default DMA mode build
 options

On 6/3/21 6:58 AM, John Garry wrote:
> From: Zhen Lei <thunder.leizhen@...wei.com>
> 
> First, add build options IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
> opportunity to set {lazy|strict} mode as default at build time. Then put
> the two config options in an choice, as they are mutually-exclusive.
> 
> [jpg: Make choice between strict and lazy only (and not passthrough)]
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>  drivers/iommu/Kconfig | 34 ++++++++++++++++++++++++++++++++++
>  drivers/iommu/iommu.c |  3 ++-
>  2 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 1f111b399bca..12ef90256df8 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -90,6 +90,40 @@ config IOMMU_DEFAULT_PASSTHROUGH
>  
>  	  If unsure, say N here.
>  
> +choice
> +	prompt "IOMMU default DMA mode"
> +	depends on IOMMU_API
> +
> +	default IOMMU_DEFAULT_STRICT
> +	help
> +	  This option allows an IOMMU DMA mode to be chosen at build time, to
> +	  override the default DMA mode of each ARCH, removing the need to
> +	  pass in kernel parameters through command line. It is still possible
> +	  to provide ARCH-specific or common boot options to override this
> +	  option.
> +
> +	  If unsure, keep the default.
> +
> +config IOMMU_DEFAULT_LAZY
> +	bool "lazy"
> +	help
> +	  Support lazy mode, where for every IOMMU DMA unmap operation, the
> +	  flush operation of IOTLB and the free operation of IOVA are deferred.
> +	  They are only guaranteed to be done before the related IOVA will be
> +	  reused.
> +
> +config IOMMU_DEFAULT_STRICT
> +	bool "strict"
> +	help
> +	  For every IOMMU DMA unmap operation, the flush operation of IOTLB and
> +	  the free operation of IOVA are guaranteed to be done in the unmap
> +	  function.
> +
> +	  This mode is safer than the two above, but it maybe slower in some

There don't seem to be two above?

> +	  high performace scenarios.

	       performance

> +
> +endchoice


thanks.
-- 
~Randy