Re: [PATCH 1/2] iommu: Add config option to set passthrough as default

["Yang, Shunyong" <shunyong.yang@hxt-semitech.com>]

Hi, Olof,

Tired of changing command line. I like this patch.

Thanks.
Shunyong. 

On Wed, 2018-07-11 at 13:59 -0700, Olof Johansson wrote:
> This allows the default behavior to be controlled by a kernel config
> option instead of changing the commandline for the kernel to include
> "iommu.passthrough=on" on machines where this is desired.
> 
> Signed-off-by: Olof Johansson <olof@lixom.net>
> ---
>  drivers/iommu/Kconfig | 10 ++++++++++
>  drivers/iommu/iommu.c |  4 ++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 689ffe538370..a9bb1a5b5e43 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -60,6 +60,16 @@ config IOMMU_IO_PGTABLE_ARMV7S_SELFTEST
>  
>  endmenu
>  
> +config IOMMU_DEFAULT_PASSTHROUGH
> +	bool "IOMMU passthrough by default"
> +	depends on IOMMU_API
> +        help
> +	  Enable passthrough by default (removing the need to pass
> in
> +	  iommu.passthrough=on through command line). If this is
> enabled,
> +	  you can still disable with iommu.passthrough=off
> +
> +	  If unsure, say N here.
> +
>  config IOMMU_IOVA
>  	tristate
>  
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 63b37563db7e..ab8fc54467e0 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -36,7 +36,11 @@
>  
>  static struct kset *iommu_group_kset;
>  static DEFINE_IDA(iommu_group_ida);
> +#ifdef CONFIG_IOMMU_DEFAULT_PASSTHROUGH
> +static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
> +#else
>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
> +#endif
>  
>  struct iommu_callback_data {
>  	const struct iommu_ops *ops;