Re: [PATCH v2 1/1] iommu/vt-d: Add Kconfig option to enable/disable scalable mode

From: Qian Cai <cai@lca.pw>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	kevin.tian@intel.com, ashok.raj@intel.com,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	jacob.jun.pan@intel.com
Subject: Re: [PATCH v2 1/1] iommu/vt-d: Add Kconfig option to enable/disable scalable mode
Date: Fri, 8 Nov 2019 22:59:01 -0500	[thread overview]
Message-ID: <A85B5322-5DED-4E58-B3BC-4DA3783BB8A6@lca.pw> (raw)
In-Reply-To: <20191109034039.27964-1-baolu.lu@linux.intel.com>

> On Nov 8, 2019, at 10:40 PM, Lu Baolu <baolu.lu@linux.intel.com> wrote:
> 
> This adds Kconfig option INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
> to make it easier for distributions to enable or disable the
> Intel IOMMU scalable mode by default during kernel build.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> drivers/iommu/Kconfig       | 9 +++++++++
> drivers/iommu/intel-iommu.c | 7 ++++++-
> 2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index e3842eabcfdd..fbdf3fd291d9 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -242,6 +242,15 @@ config INTEL_IOMMU_FLOPPY_WA
> 	  workaround will setup a 1:1 mapping for the first
> 	  16MiB to make floppy (an ISA device) work.
> 
> +config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
> +	prompt "Enable Intel IOMMU scalable mode by default"
> +	depends on INTEL_IOMMU
> +	help
> +	  Selecting this option will enable the scalable mode if
> +	  hardware presents the capability. If this option is not
> +	  selected, scalable mode support could also be enabled
> +	  by passing intel_iommu=sm_on to the kernel.

Maybe a sentence or two to describe what the scalable mode is in layman's
terms could be useful, so developers don’t need to search around for the
Kconfig selection?

> +
> config IRQ_REMAP
> 	bool "Support for Interrupt Remapping"
> 	depends on X86_64 && X86_IO_APIC && PCI_MSI && ACPI
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 6db6d969e31c..6051fe790c61 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -355,9 +355,14 @@ static phys_addr_t intel_iommu_iova_to_phys(struct iommu_domain *domain,
> int dmar_disabled = 0;
> #else
> int dmar_disabled = 1;
> -#endif /*CONFIG_INTEL_IOMMU_DEFAULT_ON*/
> +#endif /* CONFIG_INTEL_IOMMU_DEFAULT_ON */
> 
> +#ifdef INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
> +int intel_iommu_sm = 1;
> +#else
> int intel_iommu_sm;
> +#endif /* INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON */
> +
> int intel_iommu_enabled = 0;
> EXPORT_SYMBOL_GPL(intel_iommu_enabled);
> 
> -- 
> 2.17.1
> 
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