linux-kernel - Re: [PATCH v4 10/15] iommu/vt-d: Probe DMA-capable ACPI name space devices

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Date:   Mon, 3 Jun 2019 08:35:39 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>, kevin.tian@...el.com,
        ashok.raj@...el.com, dima@...sta.com, tmurphy@...sta.com,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        jacob.jun.pan@...el.com
Subject: Re: [PATCH v4 10/15] iommu/vt-d: Probe DMA-capable ACPI name space
 devices

Hi,

On 5/29/19 2:16 PM, Christoph Hellwig wrote:
> On Sat, May 25, 2019 at 01:41:31PM +0800, Lu Baolu wrote:
>> Some platforms may support ACPI name-space enumerated devices
>> that are capable of generating DMA requests. Platforms which
>> support DMA remapping explicitly declares any such DMA-capable
>> ACPI name-space devices in the platform through ACPI Name-space
>> Device Declaration (ANDD) structure and enumerate them through
>> the Device Scope of the appropriate remapping hardware unit.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> 
> Isn't this something that should be handled through the IOMMU API so
> that it covers other IOMMU types as well?
> 
> How does this scheme compare to the one implemented in
> drivers/acpi/arm64/iort.c?
> 

This part of code was added to be compatible with the past.

Yes. I've ever thought about this. But these devices sit on the acpi bus
together with other devices which are not DMA-capable. And on some
platforms these devices exist on the pci bus as well.

Best regards,
Baolu