linux-kernel - Re: [PATCH v11 0/3] Enhance IOMMU default DMA mode build options

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Date:   Thu, 10 Jun 2021 17:25:36 +0100
From:   John Garry <john.garry@...wei.com>
To:     Joerg Roedel <joro@...tes.org>
CC:     <will@...nel.org>, <dwmw2@...radead.org>,
        <baolu.lu@...ux.intel.com>, <robin.murphy@....com>,
        <linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <linuxarm@...wei.com>, <thunder.leizhen@...wei.com>,
        <chenxiang66@...ilicon.com>, <rdunlap@...radead.org>
Subject: Re: [PATCH v11 0/3] Enhance IOMMU default DMA mode build options

On 09/06/2021 09:15, Joerg Roedel wrote:
> On Tue, Jun 08, 2021 at 09:18:25PM +0800, John Garry wrote:
>> Zhen Lei (3):
>>    iommu: Enhance IOMMU default DMA mode build options
>>    iommu/vt-d: Add support for IOMMU default DMA mode build options
>>    iommu/amd: Add support for IOMMU default DMA mode build options
> So I like the idea, but can we go a step further and get (mostly) rid of
> the driver-specific setup code for lazy/non-lazy mode? This can happen
> in the dma-iommu code and the drivers only need to keep the support for
> their legacy command line options.

The AMD driver just maintains a flag and a print for the strict mode 
setting.

The Intel driver still maintains some lazy vs strict config, depending 
on the platform:
- DMAR caching mode set means that we enforce strict mode globally
- workaround for ironlake gpu means that we enforce strict mode globally

So there isn't much driver-specific setup remaining, and I can't see the 
intel stuff being moved into dma-iommu.c or asbtracted (for that).

We could prob replace the driver-specific logs with new logs in iommu.c, 
and do away with maintaining the proprietary driver strict mode flags. 
That's if we're ok with replacing the driver-specific logs, though.

Thanks,
John