linux-kernel - Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

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Message-ID: <CALiNf2-a6JpbeyfCoGdjFAbguxwW5kn1r_Oq6yr+k1rGum7O8Q@mail.gmail.com>
Date:   Thu, 14 Jan 2021 17:06:07 +0800
From:   Claire Chang <tientzu@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <joro@...tes.org>, will@...nel.org,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, grant.likely@....com,
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        mingo@...nel.org, bauerman@...ux.ibm.com, peterz@...radead.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
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        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        rdunlap@...radead.org, dan.j.williams@...el.com,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-devicetree <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        xen-devel@...ts.xenproject.org, Tomasz Figa <tfiga@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>
Subject: Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

On Wed, Jan 13, 2021 at 8:42 PM Christoph Hellwig <hch@....de> wrote:
>
> > +#ifdef CONFIG_SWIOTLB
> > +     struct io_tlb_mem       *dma_io_tlb_mem;
> >  #endif
>
> Please add a new config option for this code instead of always building
> it when swiotlb is enabled.
>
> > +static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
> > +                                size_t size)
>
> Can you split the refactoring in swiotlb.c into one or more prep
> patches?
>
> > +static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> > +                                 struct device *dev)
> > +{
> > +     struct io_tlb_mem *mem = rmem->priv;
> > +     int ret;
> > +
> > +     if (dev->dma_io_tlb_mem)
> > +             return -EBUSY;
> > +
> > +     if (!mem) {
> > +             mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> > +             if (!mem)
> > +                     return -ENOMEM;
>
> What is the calling convention here that allows for a NULL and non-NULL
> private data?

Since multiple devices can share the same pool, the private data,
io_tlb_mem struct, will be initialized by the first device attached to
it.
This is similar to rmem_dma_device_init() in kernel/dma/coherent.c.
I'll add a comment for it in next version.