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

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Date:   Mon, 11 Nov 2019 13:20:52 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Qian Cai <cai@....pw>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>, kevin.tian@...el.com,
        ashok.raj@...el.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, jacob.jun.pan@...el.com
Subject: Re: [PATCH v2 1/1] iommu/vt-d: Add Kconfig option to enable/disable
 scalable mode

Hi,

On 11/11/19 10:58 AM, Qian Cai wrote:
> 
> 
>> On Nov 8, 2019, at 10:43 PM, Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>>
>> +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.
>> +
> 
> Does it also make sense to mention which hardware presents this capability or how to check it?
> 

The scalable mode is defined in VT-d 3.0. The scalable mode capability
could be checked by reading /sys/devices/virtual/iommu/dmar*/intel-
iommu/ecap. It's currently not friendly for reading. You need to decode
it according to the spec.

Best regards,
baolu