linux-kernel - Re: [PATCH] iommu: Print default strict or lazy mode at init time

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Message-ID: <e478aea8-54d3-bfc6-1bc8-b0c7709e353a@huawei.com>
Date:   Tue, 1 Jun 2021 16:50:39 +0100
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <joro@...tes.org>,
        <will@...nel.org>
CC:     <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <hch@....de>
Subject: Re: [PATCH] iommu: Print default strict or lazy mode at init time

On 01/06/2021 10:09, Robin Murphy wrote:
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 808ab70d5df5..f25fae62f077 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -138,6 +138,11 @@ static int __init iommu_subsys_init(void)
>>           (iommu_cmd_line & IOMMU_CMD_LINE_DMA_API) ?
>>               "(set via kernel command line)" : "");
>> +    pr_info("Default DMA domain mode: %s %s\n",
> 
> Nit: I think this might be a little unclear for end-users - *I'm* not 
> even sure whether "Default" here is meant to refer to the mode setting 
> itself or to default domains (of DMA type). Maybe something like "DMA 
> domain TLB invalidation policy"? Certainly it seems like a good idea to 
> explicitly mention invalidation to correlate with the documentation of 
> the "iommu.strict" parameter.
> 
> Ack to the general idea though.

ok, so I'll go with this:

pr_info("DMA domain default TLB invalidation policy: %s mode %s\n",
               iommu_dma_strict ? "strict" : "lazy",
                (iommu_cmd_line & IOMMU_CMD_LINE_STRICT) ?
                        "(set via kernel command line)" : "");

I think it's worth mentioning "default" somewhere, as not all IOMMUs or 
devices will use lazy mode even if it's default.

Thanks,
John