linux-kernel - Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma

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Message-ID: <20191112071640.GA3343@lst.de>
Date:   Tue, 12 Nov 2019 08:16:40 +0100
From:   Christoph Hellwig <hch@....de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Christoph Hellwig <hch@....de>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        pengfei.xu@...el.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Jonathan Corbet <corbet@....net>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 02/10] iommu/vt-d: Use per-device dma_ops

On Fri, Jul 26, 2019 at 09:56:51AM +0800, Lu Baolu wrote:
> I think current code doesn't do the right thing. The user asks the iommu
> driver to use identity domain for a device, but the driver force it back
> to DMA domain because of the device address capability.
>
>> expensive.  I don't think that this change is a good idea, and even if
>> we decide that this is a good idea after all that should be done in a
>> separate prep patch that explains the rationale.
>
> Yes. Make sense.

Now that the bounce code has landed it might be good time to revisit
this patch in isolation and with a better explanation.