linux-kernel - Re: [PATCH v6 04/15] swiotlb: Add restricted DMA pool initialization

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Date:   Mon, 10 May 2021 17:02:56 +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>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        sstabellini@...nel.org, Robin Murphy <robin.murphy@....com>,
        grant.likely@....com, xypron.glpk@....de,
        Thierry Reding <treding@...dia.com>, mingo@...nel.org,
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        Randy Dunlap <rdunlap@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
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Subject: Re: [PATCH v6 04/15] swiotlb: Add restricted DMA pool
 initialization

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/of_reserved_mem.h>
> +#include <linux/slab.h>
> +#endif

I don't think any of this belongs into swiotlb.c.  Marking
swiotlb_init_io_tlb_mem non-static and having all this code in a separate
file is probably a better idea.

> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> +				    struct device *dev)
> +{
> +	struct io_tlb_mem *mem = rmem->priv;
> +	unsigned long nslabs = rmem->size >> IO_TLB_SHIFT;
> +
> +	if (dev->dma_io_tlb_mem)
> +		return 0;
> +
> +	/* Since multiple devices can share the same pool, the private data,
> +	 * io_tlb_mem struct, will be initialized by the first device attached
> +	 * to it.
> +	 */

This is not the normal kernel comment style.

> +#ifdef CONFIG_ARM
> +		if (!PageHighMem(pfn_to_page(PHYS_PFN(rmem->base)))) {
> +			kfree(mem);
> +			return -EINVAL;
> +		}
> +#endif /* CONFIG_ARM */

And this is weird.  Why would ARM have such a restriction?  And if we have
such rstrictions it absolutely belongs into an arch helper.

> +		swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
> +
> +		rmem->priv = mem;
> +
> +#ifdef CONFIG_DEBUG_FS
> +		if (!debugfs_dir)
> +			debugfs_dir = debugfs_create_dir("swiotlb", NULL);
> +
> +		swiotlb_create_debugfs(mem, rmem->name, debugfs_dir);

Doesn't the debugfs_create_dir belong into swiotlb_create_debugfs?  Also
please use IS_ENABLEd or a stub to avoid ifdefs like this.