linux-kernel - Re: [PATCH v7 13/15] dma-direct: Allocate memory from restricted DMA pool if available

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Date:   Thu, 27 May 2021 15:30:46 +0200
From:   Christoph Hellwig <hch@....de>
To:     Claire Chang <tientzu@...omium.org>
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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        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
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        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
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Subject: Re: [PATCH v7 13/15] dma-direct: Allocate memory from restricted
 DMA pool if available

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +	if (swiotlb_free(dev, page, size))
> +		return;
> +#endif

Please avoid the ifdefs by either stubbing out the function to be a no-op
or by using IS_ENABLED.

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +	page = swiotlb_alloc(dev, size);
> +	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +		__dma_direct_free_pages(dev, page, size);
> +		page = NULL;
> +	}
> +#endif

Same here, for the stub it would just return NULL.