linux-kernel - Re: [PATCH v11 09/12] swiotlb: Add restricted DMA alloc/free support

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Date:   Wed, 16 Jun 2021 07:18:39 +0200
From:   Christoph Hellwig <hch@....de>
To:     Claire Chang <tientzu@...omium.org>
Cc:     Christoph Hellwig <hch@....de>, Rob Herring <robh+dt@...nel.org>,
        mpe@...erman.id.au, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        sstabellini@...nel.org, Robin Murphy <robin.murphy@....com>,
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        Thierry Reding <treding@...dia.com>, mingo@...nel.org,
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        Saravana Kannan <saravanak@...gle.com>,
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        Randy Dunlap <rdunlap@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
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        Bjorn Helgaas <bhelgaas@...gle.com>, chris@...is-wilson.co.uk,
        Daniel Vetter <daniel@...ll.ch>, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
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Subject: Re: [PATCH v11 09/12] swiotlb: Add restricted DMA alloc/free
 support

On Wed, Jun 16, 2021 at 01:10:02PM +0800, Claire Chang wrote:
> On Wed, Jun 16, 2021 at 12:59 PM Christoph Hellwig <hch@....de> wrote:
> >
> > On Wed, Jun 16, 2021 at 12:04:16PM +0800, Claire Chang wrote:
> > > Just noticed that after propagating swiotlb_force setting into
> > > io_tlb_default_mem->force, the memory allocation behavior for
> > > swiotlb_force will change (i.e. always skipping arch_dma_alloc and
> > > dma_direct_alloc_from_pool).
> >
> > Yes, I think we need to split a "use_for_alloc" flag from the force flag.
> 
> How about splitting is_dev_swiotlb_force into is_swiotlb_force_bounce
> (io_tlb_mem->force_bounce) and is_swiotlb_force_alloc
> (io_tlb_mem->force_alloc)?

Yes, something like that.  I'd probably not use force for the alloc side
given that we otherwise never allocte from the swiotlb buffer.