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Subject: Re: [PATCH v13 6/6] iommu: Remove mode argument from
 iommu_set_dma_strict()
To:     John Garry <john.garry@huawei.com>, joro@8bytes.org,
        will@kernel.org, dwmw2@infradead.org, robin.murphy@arm.com,
        corbet@lwn.net
References: <1623841437-211832-1-git-send-email-john.garry@huawei.com>
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 <de6a2874-3d6d-ed2a-78f5-fb1fb0195228@linux.intel.com>
 <c61376c8-5285-1121-046f-3ab12eee9902@huawei.com>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <cac021f9-8469-a3b4-a0c6-80a37e882b6f@linux.intel.com>
Date:   Fri, 18 Jun 2021 09:52:29 +0800
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On 6/17/21 3:41 PM, John Garry wrote:
> 
>>> @@ -349,10 +349,9 @@ static int __init iommu_dma_setup(char *str)
>>>   }
>>>   early_param("iommu.strict", iommu_dma_setup);
>>> -void iommu_set_dma_strict(bool strict)
>>> +void iommu_set_dma_strict(void)
>>>   {
>>> -    if (strict || !(iommu_cmd_line & IOMMU_CMD_LINE_STRICT))
>>> -        iommu_dma_strict = strict;
>>> +    iommu_dma_strict = true;
>>
>> Sorry, I still can't get how iommu.strict kernel option works.
>>
>> static int __init iommu_dma_setup(char *str)
>> {
>>          int ret = kstrtobool(str, &iommu_dma_strict);
>>
>>          if (!ret)
>>                  iommu_cmd_line |= IOMMU_CMD_LINE_STRICT;
>>          return ret;
>> }
>> early_param("iommu.strict", iommu_dma_setup);
>>
>> The bit IOMMU_CMD_LINE_STRICT is only set, but not used anywhere.
> 
> It is used in patch 2/6:
> 
> +    pr_info("DMA domain TLB invalidation policy: %s mode %s\n",
> +        iommu_dma_strict ? "strict" : "lazy",
> +        (iommu_cmd_line & IOMMU_CMD_LINE_STRICT) ?
> +            "(set via kernel command line)" : "");
> 
>> Hence,
>> I am wondering how could it work? A bug or I missed anything?
> 
> It is really just used for informative purpose now.

I am clear now. Thanks!

Best regards,
baolu