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Subject: Re: [PATCH v13 6/6] iommu: Remove mode argument from
 iommu_set_dma_strict()
To:     Lu Baolu <baolu.lu@linux.intel.com>, <joro@8bytes.org>,
        <will@kernel.org>, <dwmw2@infradead.org>, <robin.murphy@arm.com>,
        <corbet@lwn.net>
CC:     <linux-kernel@vger.kernel.org>, <iommu@lists.linux-foundation.org>,
        <linuxarm@huawei.com>, <thunder.leizhen@huawei.com>,
        <chenxiang66@hisilicon.com>, <linux-doc@vger.kernel.org>
References: <1623841437-211832-1-git-send-email-john.garry@huawei.com>
 <1623841437-211832-7-git-send-email-john.garry@huawei.com>
 <de6a2874-3d6d-ed2a-78f5-fb1fb0195228@linux.intel.com>
From:   John Garry <john.garry@huawei.com>
Message-ID: <c61376c8-5285-1121-046f-3ab12eee9902@huawei.com>
Date:   Thu, 17 Jun 2021 08:41:24 +0100
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>> @@ -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.

Thanks,
john