linux-kernel - Re: [PATCH v12 3/5] iommu/vt-d: Add support for IOMMU default DMA mode build options

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Message-ID: <a4b794be-6648-c088-877d-cdf8762151f6@linux.intel.com>
Date:   Wed, 16 Jun 2021 16:42:18 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>,
        John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org
Cc:     baolu.lu@...ux.intel.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linuxarm@...wei.com,
        thunder.leizhen@...wei.com, chenxiang66@...ilicon.com
Subject: Re: [PATCH v12 3/5] iommu/vt-d: Add support for IOMMU default DMA
 mode build options

On 2021/6/15 16:25, Robin Murphy wrote:
> On 2021-06-15 08:26, Lu Baolu wrote:
>> Hi John,
>>
>> On 6/14/21 4:03 PM, John Garry wrote:
>>> On 12/06/2021 03:14, Lu Baolu wrote:
>>>> On 2021/6/11 20:20, John Garry wrote:
>>>>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>>>>> index 2a71347611d4..4467353f981b 100644
>>>>> --- a/drivers/iommu/Kconfig
>>>>> +++ b/drivers/iommu/Kconfig
>>>>> @@ -94,6 +94,7 @@ choice
>>>>>       prompt "IOMMU default DMA mode"
>>>>>       depends on IOMMU_DMA
>>>>> +    default IOMMU_DEFAULT_LAZY if INTEL_IOMMU
>>>>>       default IOMMU_DEFAULT_STRICT
>>>>
>>>> If two default values are different. Which one will be overridden?
>>>
>>> If I understand your question correctly, I think you are asking if 
>>> both are set:
>>> CONFIG_IOMMU_DEFAULT_LAZY=y
>>> CONFIG_IOMMU_DEFAULT_STRICT=y
>>>
>>> If this happens, then make defconfig complains about both being set, 
>>> and selects the 2nd, whatever that is.
>>
>> On x86, Intel or AMD, this will be
>>
>>      prompt "IOMMU default DMA mode"
>>        depends on IOMMU_DMA
>>        default IOMMU_DEFAULT_LAZY
>>        default IOMMU_DEFAULT_STRICT
>>
>> which will be default, LAZY or STRICT? Will it cause complains?
> 
> See Documentation/kbuild/kconfig-language.rst:
> 
>    A config option can have any number of default values. If multiple
>    default values are visible, only the first defined one is active.

Get it. Thank you, Robin.

Best regards,
baolu