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

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Date:   Wed, 13 Jan 2021 13:42:09 +0100
From:   Christoph Hellwig <hch@....de>
To:     Claire Chang <tientzu@...omium.org>
Cc:     robh+dt@...nel.org, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, joro@...tes.org, will@...nel.org,
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        sstabellini@...nel.org, hch@....de, m.szyprowski@...sung.com,
        robin.murphy@....com, grant.likely@....com, xypron.glpk@....de,
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Subject: Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

> +#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?