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

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Date:   Wed, 6 Jan 2021 13:52:41 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Claire Chang <tientzu@...omium.org>
Cc:     robh+dt@...nel.org, mpe@...erman.id.au, benh@...nel.crashing.org,
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Subject: Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

Hello!

In this file:

> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index e4368159f88a..7fb2ac087d23 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
..

> +static const struct reserved_mem_ops rmem_swiotlb_ops = {
> +	.device_init	= rmem_swiotlb_device_init,
> +	.device_release	= rmem_swiotlb_device_release,
> +};
> +
> +static int __init rmem_swiotlb_setup(struct reserved_mem *rmem)
> +{
> +	unsigned long node = rmem->fdt_node;
> +
> +	if (of_get_flat_dt_prop(node, "reusable", NULL) ||
> +	    of_get_flat_dt_prop(node, "linux,cma-default", NULL) ||
> +	    of_get_flat_dt_prop(node, "linux,dma-default", NULL) ||
> +	    of_get_flat_dt_prop(node, "no-map", NULL))
> +		return -EINVAL;
> +
> +	rmem->ops = &rmem_swiotlb_ops;
> +	pr_info("Reserved memory: created device swiotlb memory pool at %pa, size %ld MiB\n",
> +		&rmem->base, (unsigned long)rmem->size / SZ_1M);
> +	return 0;
> +}
> +
> +RESERVEDMEM_OF_DECLARE(dma, "restricted-dma-pool", rmem_swiotlb_setup);

The code should be as much as possible arch-agnostic. That is why there
are multiple -swiotlb files scattered in arch directories that own the
architecture specific code.

Would it be possible to move the code there and perhaps have a ARM
specific front-end for this DMA restricted pool there? See for example
the xen-swiotlb code.

Cheers!

Konrad