linux-kernel - Re: [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free support.

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Date:   Tue, 12 Jan 2021 15:41:46 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Claire Chang <tientzu@...omium.org>, robh+dt@...nel.org,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        joro@...tes.org, will@...nel.org, frowand.list@...il.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
        jgross@...e.com, sstabellini@...nel.org, hch@....de,
        m.szyprowski@...sung.com, robin.murphy@....com
Cc:     grant.likely@....com, xypron.glpk@....de, treding@...dia.com,
        mingo@...nel.org, bauerman@...ux.ibm.com, peterz@...radead.org,
        gregkh@...uxfoundation.org, saravanak@...gle.com,
        rafael.j.wysocki@...el.com, heikki.krogerus@...ux.intel.com,
        andriy.shevchenko@...ux.intel.com, rdunlap@...radead.org,
        dan.j.williams@...el.com, bgolaszewski@...libre.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, tfiga@...omium.org,
        drinkcat@...omium.org
Subject: Re: [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free
 support.

On 1/5/21 7:41 PM, Claire Chang wrote:
> Add the functions, swiotlb_alloc and swiotlb_free to support the
> memory allocation from restricted DMA pool.
> 
> Signed-off-by: Claire Chang <tientzu@...omium.org>
> ---

[snip]

> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 30ccbc08e229..126e9b3354d6 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -137,6 +137,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	void *ret;
>  	int err;
>  
> +#ifdef CONFIG_SWIOTLB
> +	if (unlikely(dev->dma_io_tlb_mem))
> +		return swiotlb_alloc(dev, size, dma_handle, attrs);
> +#endif

While this is potentially a hot path, I am not sure of the unkikely is
warranted, maybe best left as a plain conditional.
-- 
Florian