linux-kernel - Re: [PATCH v6 08/15] swiotlb: Bounce data from/to restricted DMA pool if available

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Date:   Wed, 12 May 2021 00:42:15 +0800
From:   Claire Chang <tientzu@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
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Subject: Re: [PATCH v6 08/15] swiotlb: Bounce data from/to restricted DMA pool
 if available

On Mon, May 10, 2021 at 11:05 PM Christoph Hellwig <hch@....de> wrote:
>
> > +static inline bool is_dev_swiotlb_force(struct device *dev)
> > +{
> > +#ifdef CONFIG_DMA_RESTRICTED_POOL
> > +     if (dev->dma_io_tlb_mem)
> > +             return true;
> > +#endif /* CONFIG_DMA_RESTRICTED_POOL */
> > +     return false;
> > +}
> > +
>
> >       /* If SWIOTLB is active, use its maximum mapping size */
> >       if (is_swiotlb_active(dev) &&
> > -         (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
> > +         (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE ||
> > +          is_dev_swiotlb_force(dev)))
>
> This is a mess.  I think the right way is to have an always_bounce flag
> in the io_tlb_mem structure instead.  Then the global swiotlb_force can
> go away and be replace with this and the fact that having no
> io_tlb_mem structure at all means forced no buffering (after a little
> refactoring).

Will do in the next version.